Semiconductor device and touch panel

ABSTRACT

A touch panel including an oxide semiconductor film having conductivity is provided. The touch panel includes a transistor, a second insulating film, and a touch sensor. The transistor includes a gate electrode; a gate insulating film; a first oxide semiconductor film; a source electrode and a drain electrode; a first insulating film; and a second oxide semiconductor film. The second insulating film is over the second oxide semiconductor film so that the second oxide semiconductor film is positioned between the first insulating film and the second insulating film. The touch sensor includes a first electrode and a second electrode. One of the first and second electrodes includes the second oxide semiconductor film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to a semiconductordevice. One embodiment of the present invention relates to a touchpanel. One embodiment of the present invention relates to a displaydevice. One embodiment of the present invention relates to aninput/output device. One embodiment of the present invention relates toan input device.

Note that one embodiment of the present invention is not limited to theabove technical field. One embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or amanufacturing method. One embodiment of the present invention relates toa process, a machine, manufacture, or a composition of matter.Specifically, examples of the technical field of one embodiment of thepresent invention disclosed in this specification and the like include asemiconductor device, a display device, a light-emitting device, a powerstorage device, a memory device, an electronic device, a lightingdevice, an input device, an input/output device, a driving methodthereof, and a manufacturing method thereof.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an input device, an input/output device, an electro-opticaldevice, a power generation device (including a thin film solar cell, anorganic thin film solar cell, and the like), and an electronic devicemay each include a semiconductor device.

2. Description of the Related Art

Transistors used for most flat panel displays typified by a liquidcrystal display device and a light-emitting display device are formedusing silicon semiconductors such as amorphous silicon, single crystalsilicon, and polycrystalline silicon provided over glass substrates.Further, such a transistor employing such a silicon semiconductor isused in integrated circuits (ICs) and the like.

In recent years, attention has been drawn to a technique in which,instead of a silicon semiconductor, a metal oxide exhibitingsemiconductor characteristics is used in transistors. Note that in thisspecification, a metal oxide exhibiting semiconductor characteristics isreferred to as an oxide semiconductor. For example, such a technique isdisclosed that a transistor is manufactured using zinc oxide or anIn—Ga—Zn-based oxide as an oxide semiconductor and the transistor isused as a switching element or the like in a pixel of a display device(see Patent Documents 1 and 2). Various touch sensors have beendeveloped (see Patent Documents 3 to 7).

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-96055-   [Patent Document 3] Japanese Published Patent Application No.    2011-197685-   [Patent Document 4] Japanese Published Patent Application No.    2014-44537-   [Patent Document 5] Japanese Published Patent Application No.    2014-178847-   [Patent Document 6] U.S. Pat. No. 7,920,129-   [Patent Document 7] Japanese Published Patent Application No.    2009-244958

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide atouch panel including an oxide semiconductor film having conductivity.Another object is to provide a touch panel having a simple structure.Another object is to provide a novel input device. Another object is toprovide a novel input/output device.

One embodiment of the present invention is a semiconductor deviceincluding a transistor, a second insulating film, and a touch sensor.The transistor includes a gate electrode; a gate insulating film incontact with the gate electrode; a first oxide semiconductor film thatis in contact with the gate insulating film and overlaps with the gateelectrode; a source electrode and a drain electrode that areelectrically connected to the first oxide semiconductor film; a firstinsulating film over the first oxide semiconductor film, the sourceelectrode, and the drain electrode; and a second oxide semiconductorfilm that is over the first insulating film and overlaps with the firstoxide semiconductor film. The second insulating film is over the secondoxide semiconductor film so that the second oxide semiconductor film ispositioned between the first insulating film and the second insulatingfilm. The touch sensor includes a first electrode and a secondelectrode. One of the first and second electrodes includes a third oxidesemiconductor film. The second oxide semiconductor film and the thirdoxide semiconductor film are formed in the same layer.

In the above semiconductor device, the thickness of each of the secondoxide semiconductor film and the third oxide semiconductor film ispreferably greater than or equal to 30 nm and less than or equal to 70nm.

According to another embodiment of the present invention, in the abovesemiconductor device, the first oxide semiconductor film, the secondoxide semiconductor film, and the third oxide semiconductor film areeach an In-M-Zn oxide (M is Al, Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf).

According to another embodiment of the present invention, in the abovesemiconductor device, the first insulating film includes oxygen and thesecond insulating film includes hydrogen.

According to another embodiment of the present invention, the abovesemiconductor device further includes a capacitor that includes thesecond insulating film between a pair of electrodes. The capacitortransmits visible light, and one of the pair of electrodes of thecapacitor includes the third oxide semiconductor film.

According to another embodiment of the present invention, in the abovesemiconductor device, the first and second electrodes each include thethird oxide semiconductor film.

Another embodiment of the present invention is a touch panel includingthe above semiconductor device, a conductive film, and a liquid crystalelement. The conductive film serves as a pixel electrode. The thirdoxide semiconductor film serves as a common electrode. The other of thepair of electrodes of the capacitor includes the conductive film.

Another embodiment of the present invention is a touch panel includingthe above semiconductor device and a light-emitting element. Thelight-emitting element includes a lower electrode, an upper electrode,and an EL layer positioned between the lower electrode and the upperelectrode.

According to another embodiment of the present invention, in the abovetouch panel, the first and second electrodes each include the thirdoxide semiconductor film.

According to another embodiment of the present invention, in the abovetouch panel, the other of the first and second electrodes serves as theupper electrode.

Another embodiment of the present invention is an electronic deviceincluding the above semiconductor device, and a switch, a speaker, adisplay portion, or a housing.

Another embodiment of the present invention is an electronic deviceincluding the above touch panel, and a switch, a speaker, a displayportion, or a housing.

According to one embodiment of the present invention, a touch panelincluding an oxide semiconductor film having conductivity, a touch panelhaving a simple structure, a novel input device, or a novel input/outputdevice can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a block diagram and a timing chart of a touch sensorof one embodiment.

FIGS. 2A and 2B each illustrate pixels provided with a touch sensor ofone embodiment.

FIG. 3 illustrates pixels provided with a touch sensor of oneembodiment.

FIGS. 4A and 4B each illustrate pixels provided with a touch sensor ofone embodiment.

FIGS. 5A to 5C illustrate operations of touch sensors and pixels of oneembodiment.

FIGS. 6A to 6D are schematic cross-sectional views illustrating modes ofa touch panel of one embodiment.

FIGS. 7A to 7C are perspective views illustrating an example of a touchpanel of one embodiment.

FIG. 8 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 9 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 10 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIG. 11 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIGS. 12A and 12B are each a top view illustrating a structure ofelectrodes of a touch sensor of one embodiment.

FIG. 13 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 14 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIG. 15 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 16 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 17 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIG. 18 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 19 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIG. 20 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 21 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIG. 22 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 23 is a cross-sectional view illustrating an example of a touchpanel of one embodiment.

FIG. 24 is a top view illustrating a structure of electrodes of a touchsensor of one embodiment.

FIGS. 25A to 25D are cross-sectional views illustrating a method formanufacturing a transistor and the like of one embodiment.

FIGS. 26A to 26C are cross-sectional views illustrating a method formanufacturing a transistor and the like of one embodiment.

FIGS. 27A to 27C are cross-sectional views illustrating a method formanufacturing a transistor and the like of one embodiment.

FIG. 28 is a cross-sectional view illustrating a method formanufacturing a transistor and the like of one embodiment.

FIGS. 29A and 29B are each a cross-sectional view illustrating astructure of a transistor and the like of one embodiment.

FIGS. 30A to 30C are Cs-corrected high-resolution TEM images of a crosssection of a CAAC-OS, and FIG. 30D is a schematic cross-sectional viewof a CAAC-OS.

FIGS. 31A to 31D are Cs-corrected high-resolution TEM images of a planeof a CAAC-OS.

FIGS. 32A to 32C show structural analysis of a CAAC-OS and a singlecrystal oxide semiconductor by XRD.

FIGS. 33A and 33B each show an electron diffraction pattern of aCAAC-OS.

FIG. 34 shows a change in crystal parts of an In—Ga—Zn oxide due toelectron irradiation.

FIG. 35 illustrates a deposition method of a CAAC-OS.

FIGS. 36A to 36C illustrate an InMZnO₄ crystal.

FIGS. 37A to 37F illustrate a deposition method of a CAAC-OS.

FIGS. 38A to 38C are a top view and cross-sectional views illustratingan example of a transistor.

FIGS. 39A to 39D are cross-sectional views illustrating examples of atransistor.

FIGS. 40A and 40B each show a band structure.

FIGS. 41A to 41D are cross-sectional views illustrating examples of atransistor.

FIGS. 42A and 42B illustrate structure examples of light-emittingelements.

FIG. 43 illustrates a display module of one embodiment.

FIGS. 44A to 44H each illustrate an electronic device of one embodiment.

FIGS. 45A and 45B each illustrate an electronic device of oneembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments are described in detail with reference to the drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that the mode anddetails can be variously changed without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and the description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing referred to in this specification, the size,the layer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such a scale.

In this specification and the like, ordinal numbers such as “first” and“second” are used in order to avoid confusion among components and donot limit the components numerically.

Note that the terms “film” and “layer” can be interchanged with eachother in some cases. For example, in some cases, the term “conductivefilm” can be used instead of the term “conductive layer,” and the term“insulating film” can be used instead of the term “insulating layer.”

In this specification and the like, a “semiconductor” includescharacteristics of an “insulator” in some cases when the conductivity issufficiently low, for example. Further, a “semiconductor” and an“insulator” cannot be strictly distinguished from each other in somecases because a border between the “semiconductor” and the “insulator”is not clear. Accordingly, a “semiconductor” in this specification andthe like can be called an “insulator” in some cases. Similarly, an“insulator” in this specification and the like can be called a“semiconductor” in some cases.

In this specification and the like, a “semiconductor” includescharacteristics of a “conductor” in some cases when the conductivity issufficiently high, for example. Further, a “semiconductor” and a“conductor” cannot be strictly distinguished from each other in somecases because a border between the “semiconductor” and the “conductor”is not clear. Accordingly, a “semiconductor” in this specification andthe like can be called a “conductor” in some cases. Similarly, a“conductor” in this specification and the like can be called a“semiconductor” in some cases.

Note that functions of a “source” and a “drain” of a transistor aresometimes replaced with each other when a transistor of oppositepolarity is used or when the direction of current flowing is changed incircuit operation, for example. Therefore, the terms “source” and“drain” can be used to denote the drain and the source, respectively, inthis specification.

In this specification and the like, patterning is assumed to beperformed by a photolithography process. Note that the patterning is notlimited to a photolithography process and processes other than thephotolithography process can be employed. Further, a mask formed in thephotolithography process is removed after etching treatment.

Embodiment 1

This embodiment describes driving methods, modes, structure examples ofa touch sensor or a touch panel of one embodiment of the presentinvention and structure examples of a semiconductor device of oneembodiment of the present invention with reference to drawings.

Example of Sensing Method of Sensor

FIG. 1A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 1A illustrates a pulse voltage outputcircuit 601 and a current sensing circuit 602. In FIG. 1A, as anexample, six wirings X1 to X6 represent electrodes 621 to which a pulsevoltage is applied, and six wirings Y1 to Y6 represent electrodes 622that sense changes in current. The number of such electrodes is notlimited to those illustrated in this example. FIG. 1A also illustrates acapacitor 603 that is formed with the electrodes 621 and 622 overlappingwith each other or being provided close to each other. Note that thefunctions of the electrodes 621 and 622 can be interchanged with eachother.

The pulse voltage output circuit 601 is, for example, a circuit forsequentially applying a pulse voltage to the wirings X1 to X6. Byapplying a pulse voltage to the wirings X1 to X6, an electric field isgenerated between the electrodes 621 and 622 of the capacitors 603. Witha pulse voltage, current flows through the capacitor 603. An electricfield generated between the electrodes 621 and 622 is changed by beingblocked, for example, when a finger or a stylus touches the touchsensor. That is, for example, by touch with a finger or a stylus, thecapacitance of the capacitor 603 is changed. By utilizing the change incapacitance caused by touch with a finger or a stylus as describedabove, the approach or contact of an object can be detected.

The current sensing circuit 602 is a circuit for sensing changes incurrent flowing through the wirings Y1 to Y6 that are caused by thechanges in capacitance of the capacitors 603. No change in the currentvalues of the wirings Y1 to Y6 is sensed when there is no approach orcontact of an object, whereas a decrease in the current value is sensedwhen capacitance is decreased owing to the approach or contact of anobject. In order to sense a change in current, the total amount ofcurrent may be sensed. In that case, an integrator circuit or the likemay be used to sense the total amount of current. Alternatively, thepeak value of current may be sensed. In that case, current may beconverted into voltage, and the peak value of voltage may be sensed.

FIG. 1B is a timing chart showing input and output waveforms of themutual capacitive touch sensor illustrated in FIG. 1A. In FIG. 1B,detection of an object is performed in all the rows and columns in oneframe period. FIG. 1B shows a period during which an object is notdetected (not touched) and a period during which an object is detected(touched). Sensed current values of the wirings Y1 to Y6 are shown aswaveforms of voltage values. Note that a display panel performs displayoperation. The timing of the display operation in the display panel ispreferably in synchronization with the timing of the sensing operationin the touch sensor. FIG. 1B shows an example in which these timings arenot in synchronization.

A pulse voltage is sequentially applied to the wirings X1 to X6, and thewaveforms of the wirings Y1 to Y6 change in accordance with the pulsevoltage. When there is no approach or contact of an object, thewaveforms of the wirings Y1 to Y6 change in accordance with changes inthe voltages of the wirings X1 to X6. In contrast, the current value isdecreased at the point of approach or contact of an object; accordingly,the waveform of the voltage value also changes.

By sensing a change in capacitance in this manner, the approach orcontact of an object can be detected. Even when an object such as afinger or a stylus does not touch but only approaches a touch sensor ora touch panel, a signal may be sensed in some cases.

It is preferable that, as an example, the pulse voltage output circuit601 and the current sensing circuit 602 be formed in one IC. Forexample, the IC is preferably mounted on a touch panel or a substrate ina housing of an electronic device. In the case where the touch panel hasflexibility, parasitic capacitance might be increased in a bent portionof the touch panel, and the influence of noise might be increased. Inview of this, it is preferable to use an IC to which a driving methodless influenced by noise is applied. For example, it is preferable touse an IC to which a driving method capable of increasing a signal-noiseratio (S/N ratio) is applied.

Although FIG. 1A illustrates, as a touch sensor, the structure of apassive matrix touch sensor in which only the capacitor 603 is providedat the intersection of wirings, an active matrix touch sensor includinga transistor and a capacitor may also be used.

Structure Example of In-Cell Touch Panel

An example in which at least one of electrodes included in a touchsensor is formed over a substrate provided with a display element, atransistor, and the like (hereinafter also referred to as an elementsubstrate) is described below.

A structure example of a touch panel incorporating a touch sensor into adisplay portion including a plurality of pixels (i.e., an in-cell touchpanel) is described below. An example in which a liquid crystal elementis used as a display element provided in the pixel is described.However, one embodiment of the present invention is not limited thereto,and any of various display elements can be used.

FIG. 2A is an equivalent circuit diagram of part of a pixel circuitprovided in a display portion of a touch panel in this structureexample.

Each pixel includes at least a transistor 63 and a liquid crystalelement 64. Each pixel further includes a storage capacitor in somecases. A gate of the transistor 63 is electrically connected to a wiring61, and one of a source and a drain of the transistor 63 is electricallyconnected to a wiring 62.

The pixel circuit includes a plurality of wirings extending in the Xdirection (e.g., a wiring 72_1 and a wiring 72_2) and a plurality ofwirings extending in the Y direction (e.g., a wiring 71_1 and a wiring71_2). They are provided to intersect with each other, and capacitanceis formed therebetween. The wirings 71_1 and 71_2 can be formed at thesame time as one electrode of the liquid crystal element 64 byprocessing one conductive film. The wirings 72 can be provided over asubstrate facing the element substrate (hereinafter referred to as acounter substrate). The wirings 72 may be provided over the elementsubstrate.

For example, among the pixels provided in the pixel circuit, electrodeson one side of liquid crystal elements 64 of some pixels adjacent toeach other are electrically connected to each other to form one block.For example, a plurality of linear blocks extending in the Y direction(e.g., a block 65_1 and a block 65_2) are formed here. Although onlypart of the pixel circuit is illustrated in FIG. 2A, these blocks arerepeatedly arranged in the X direction.

With the above structure, the one electrode of the liquid crystalelement in the pixel circuit can also serve as an electrode included ina touch sensor. In FIG. 2A, the wirings 71_1 and 71_2 each serve as theelectrode included in the touch sensor as well as the one electrode ofthe liquid crystal element. In contrast, the wirings 72_1 and 72_2 eachserve only as an electrode included in the touch sensor. In this manner,the structure of the touch panel can be simplified. Although theplurality of wirings extending in the Y direction (e.g., the wirings71_1 and 71_2) each serve as the electrode included in the touch sensoras well as the one electrode of the liquid crystal element in FIG. 2A,one embodiment of the present invention is not limited thereto. Forexample, the plurality of wirings extending in the X direction (e.g.,the wirings 72_1 and 72_2) may each serve as the electrode included inthe touch sensor as well as the one electrode of the liquid crystalelement. An example of a circuit diagram in that case is shown in FIG.2B.

As illustrated in FIG. 3, a configuration including a plurality ofwirings (e.g., wirings 66_1 to 66_4) that are each electricallyconnected to the one electrode of the liquid crystal element 64 may beemployed. In FIG. 3, a plurality of linear blocks (e.g., the blocks 65_1and 65_2) that extend in the Y direction are formed. These blocks 65 arerepeatedly arranged in the X direction. Moreover, a plurality of linearblocks (e.g., blocks 67_1 to 67_4) that extend in the X direction whilestepping over the plurality of linear blocks that extend in the Ydirection are formed. These blocks 67 are repeatedly arranged in the Ydirection. The wirings 66_1 to 66_4 are formed at the same time as thewiring 61 by processing one conductive film; thus, the steps formanufacturing a touch panel can be simplified.

Although FIGS. 2A and 2B and FIG. 3 each illustrate the example in whichthe liquid crystal element is used as a display element, one embodimentof the present invention is not limited thereto. FIGS. 4A and 4B eachillustrate an example in which a light-emitting element is used as adisplay element.

FIG. 5A is an equivalent circuit diagram illustrating the connectionbetween a plurality of wirings 72 extending in the X direction and aplurality of wirings 71 extending in the Y direction. In the circuitdiagram, the touch sensor is a projected mutual capacitive touch sensor.Input voltage (or selection voltage) or a common potential (or a groundpotential or a reference potential) can be input to each of the wirings71 extending in the Y direction. A ground potential (or a referencepotential) can be input to each of the wirings 72 extending in the Xdirection, or the wirings 72 can be electrically connected to a sensingcircuit. Note that the wirings 71 and the wirings 72 can be interchangedwith each other. That is, the wirings 71 can be electrically connectedto the sensing circuit.

Operation of the above-described touch panel is described below withreference to FIGS. 5B and 5C.

For example, one frame period is divided into a writing period and asensing period. The writing period is a period during which image datais written to a pixel and the wirings 72 (also referred to as gate linesor scan lines) are sequentially selected. The sensing period is a periodduring which sensing is performed by the touch sensor and the wirings 71extending in the Y direction are sequentially selected and input voltageis input.

FIG. 5B is an equivalent circuit diagram in the writing period. In thewiring period, a common potential is input to both the wirings 72extending in the X direction and the wirings 71 extending in the Ydirection.

FIG. 5C is an equivalent circuit diagram at some point in time in thesensing period. In the sensing period, input voltage is input to each ofthe wirings 71 extending in the Y direction. The wirings 72 extending inthe X direction that are selected are electrically connected to thesensing circuit, and a common potential is input to the wirings 72extending in the X direction that are not selected.

Note that the driving method described here can be applied not only tothe in-cell touch panel but also to touch panels having otherstructures.

It is preferable that the period during which an image is written andthe period during which sensing is performed by the touch sensor beseparately provided as described above. For example, sensing ispreferably performed in a blanking period. In this manner, a decrease insensitivity of the touch sensor caused by noise generated when an imageis written to a pixel can be suppressed.

Examples of Touch Panel

Examples of a touch panel of one embodiment of the present invention aredescribed below.

Note that in this specification and the like, a touch panel has afunction of displaying or outputting an image or the like on or to adisplay surface and a function of a touch sensor capable of detectingthe approach or contact of an object such as a finger or a stylus to thedisplay surface. Therefore, the touch panel is one embodiment of aninput/output device.

In this specification and the like, a structure in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a substrate of a touch panel, or a structure in which anintegrated circuit (IC) is mounted on a substrate by a chip on glass(COG) method is referred to as a touch panel module or a display module,or simply referred to as a touch panel in some cases.

A capacitive touch sensor that can be used for one embodiment of thepresent invention includes a pair of conductive films. Capacitance isformed between the pair of conductive films. The capacitance between thepair of conductive films changes when an object touches or approachesthe pair of conductive films. Utilizing this change, detection can beperformed.

Examples of the capacitive touch sensor include a surface capacitivetouch sensor and a projected capacitive touch sensor. Examples of theprojected capacitive touch sensor include a self capacitive touch sensorand a mutual capacitive touch sensor, which differ mainly in the drivingmethod. The use of a mutual capacitive touch sensor is preferablebecause multiple points can be detected simultaneously.

As a display element in a touch panel of one embodiment of the presentinvention, a variety of display elements, for example, a liquid crystalelement (using a vertical electric field mode or a horizontal electricfield mode), an optical element utilizing micro electro mechanicalsystems (MEMS), a light-emitting element such as an organicelectroluminescence (EL) element or a light-emitting diode (LED), and anelectrophoretic element can be used.

Here, a transmissive liquid crystal display device including a liquidcrystal element using a horizontal electric field mode as a displayelement is preferably used for the touch panel.

One or both of a pair of substrates in a touch panel of one embodimentof the present invention include a pair of electrodes (also referred toas conductive films or wirings) included in a touch sensor. Thus, thetouch panel has a structure in which a display panel and the touchsensor are combined. Therefore, the thickness of the touch panel isreduced, leading to a lightweight touch panel.

FIG. 6A is a schematic cross-sectional view illustrating a mode of atouch panel 10 of one embodiment of the present invention.

The touch panel 10 includes a substrate 11, a substrate 12, an FPC 13, aconductive film 14, a liquid crystal element 20, a coloring film 31, aconductive film 41, and the like.

The liquid crystal element 20 includes a conductive film 21, aconductive film 22, and liquid crystal 23. In the example illustratedhere, a liquid crystal element using a fringe field switching (FFS) modeis used as the liquid crystal element 20. The conductive film 22 ispositioned over the conductive film 21 with an insulating film 24provided therebetween. For example, the conductive film 22 has acomb-like top shape or a top shape provided with a slit (a top shape isalso referred to as a planar shape). One of the conductive films 21 and22 functions as a common electrode, and the other functions as a pixelelectrode. In the case where a light-emitting element or the like isused as a display element, for example, the conductive film 22 does nothave a comb-like top shape or a top shape provided with a slit.

The touch sensor can conduct detection using capacitance formed betweenthe conductive film 41 provided on the substrate 12 side and theconductive film 21 serving as one of a pair of electrodes of the liquidcrystal element 20. With such a structure, the one electrode of theliquid crystal element 20 can also serve as one of a pair of electrodesof the touch sensor. Thus, the processing steps can be simplified,leading to an improvement in yield and a reduction in manufacturingcost. Note that the conductive film 41 is formed over a surface of thesubstrate 12 on the display surface side (the side opposite to thesubstrate 11). In addition, the conductive film 41 is electricallyconnected to an FPC 43 provided on the substrate 12 side. The conductivefilm 21 is electrically connected to the FPC 13 provided on thesubstrate 11 side via the conductive film 14.

The touch panel 10 illustrated in FIG. 6B has a structure without theconductive film 41 and the FPC 43. Conductive films 21 a and 21 bserving as the common electrode of the liquid crystal element 20 alsoserve as the pair of electrodes of the touch sensor. With such astructure, the processing steps can be simpler than those of thestructure illustrated in FIG. 6A. Note that the conductive film 21 a iselectrically connected to the FPC 13 via the conductive film 14, and theconductive film 21 b is electrically connected to the FPC 13 via aconductive film that is not illustrated.

Note that FIGS. 6A and 6B illustrate examples in which the electrode(the conductive films 21, 21 a, and 21 b) that is positioned in a lowerlayer of the pair of electrodes forming the liquid crystal element 20 isa common electrode; however, one embodiment of the present invention isnot limited to these examples. FIGS. 6C and 6D illustrate respectivemodification examples of FIGS. 6A and 6B. In FIGS. 6C and 6D, theelectrode (the conductive film 22) that is positioned in an upper layerof the pair of electrodes forming the liquid crystal element 20 is acommon electrode.

The above is the description of examples of the touch panel.

Structure Example 1

More specific structure examples of the touch panel are described below.

FIG. 7A is a schematic perspective view of a touch panel 310 of oneembodiment of the present invention. FIGS. 7B and 7C are schematicperspective developed views of FIG. 7A. FIG. 7B is a schematicperspective view of the counter substrate side, and FIG. 7C is aschematic perspective view of the element substrate side. Note that onlymain components are illustrated for simplicity.

The touch panel 310 includes a substrate 102 and a substrate 372 thatare provided so as to face each other.

A display portion 381, a driver circuit 382, a wiring 386, a drivercircuit 384, and the like are provided over the substrate 102 (see FIG.7C). An oxide semiconductor film 111 is formed in the display portion381. The substrate 102 is provided with an FPC 373 that is electricallyconnected to the wiring 386. In the example illustrated in FIGS. 7A and7C, an IC 374 is provided over the FPC 373.

A plurality of conductive films 334, a plurality of conductive films335, a plurality of conductive films 341, and the like are provided on asurface of the substrate 372 that is the side opposite to the substrate102 (see FIG. 7B). Each of the conductive films 341 is electricallyconnected to one of the plurality of conductive films 334. An FPC 375that is electrically connected to the plurality of conductive films 341is provided over the substrate 372.

The conductive film 335 is provided between the two conductive films334. With the conductive film 335, the generation of a differencebetween the transmittance of a region where the conductive film 334 isprovided and the transmittance of a region where the conductive film 334is not provided can be suppressed. The conductive film 335 is preferablyelectrically floating. With this structure, a change in the potential ofone of the conductive film 334 and the oxide semiconductor film 111 canbe efficiently transmitted to the other through the conductive film 335,thereby increasing the detection sensitivity. The conductive film 335 isnot necessarily provided, when it is not needed.

The display portion 381 includes at least a plurality of pixels (seeFIG. 7C). Each of the pixels includes at least one display element. Itis preferable that each of the pixels include a transistor and a displayelement. As the display element, typically, a light-emitting elementsuch as an organic EL element, a liquid crystal element, or the like canbe used. In this structure example, a liquid crystal element is used asthe display element.

As the driver circuit 382, for example, a circuit functioning as a scanline driver circuit, a signal line driver circuit, or the like can beused.

The wiring 386 has a function of supplying a signal or electric power tothe display portion 381 or the driver circuit 382. The signal or theelectric power is input from the outside or the IC 374 to the wiring 386through the FPC 373.

The driver circuit 384 has a function of sequentially selecting theoxide semiconductor film 111. When the touch sensor is driven bysequentially selecting not the oxide semiconductor film 111 but theconductive films 334, the driver circuit 384 has a function of switchinga fixed potential and a sensing signal and supplying it to the oxidesemiconductor film 111. In the case where a signal for driving the touchsensor is supplied from the IC 374 or the outside, the driver circuit384 is not necessarily provided.

In the example illustrated in FIGS. 7A to 7C, the IC 374 is mounted onthe FPC 373 by a chip-on-film (COF) method. As the IC 374, for example,an IC functioning as a scan line driver circuit or a signal line drivercircuit can be used. Note that it is possible that the IC 374 is notprovided when the touch panel 310 includes circuits functioning as ascan line driver circuit and a signal line driver circuit or whencircuits functioning as a scan line driver circuit and a signal linedriver circuit are provided outside and a signal for driving the displayportion 381 is input through the FPC 373. The IC 374 may also bedirectly mounted on the substrate 102 by a chip-on-glass (COG) method orthe like.

The IC 374 can have a function of driving the touch sensor.Alternatively, an IC for driving the touch sensor may further beprovided. Further alternatively, an IC for driving the touch sensor maybe mounted on the substrate 102.

The touch sensor includes the conductive film 334 that is provided overthe substrate 372 and the oxide semiconductor film 111 that is providedover the substrate 102. With the use of capacitance formed between theconductive film 334 and the oxide semiconductor film 111, the approachor contact of an object can be sensed.

[Cross-Sectional Structure Example 1]

Examples of the cross-sectional structure of a touch panel of oneembodiment of the present invention are described below with referenceto the drawings.

FIG. 8 is a schematic cross-sectional view of the touch panel 310. FIG.8 illustrates the cross sections of a region including the FPCs 373 and375, a region including the driver circuit 382, and a region includingthe display portion 381 in FIG. 7A.

The substrate 102 and the substrate 372 are attached to each other witha sealant 151. A region surrounded by the substrate 102, the substrate372, and the sealant 151 is filled with liquid crystal 353.

The touch panel 310 illustrated in FIG. 8 includes, in the displayportion 381, a transistor 150 including an oxide semiconductor film 110and a capacitor 160 including an insulating film between a pair ofelectrodes. Note that in the capacitor 160, one of the pair ofelectrodes is the oxide semiconductor film 111, and the other of thepair of electrodes is a conductive film 120.

The transistor 150 includes a gate electrode 104 over a substrate 102,an insulating film 108 serving as a gate insulating film over the gateelectrode 104, the oxide semiconductor film 110 overlapping with thegate electrode 104 over the insulating film 108, and a source electrode112 a and a drain electrode 112 b over the oxide semiconductor film 110.In other words, the transistor 150 includes the oxide semiconductor film110, the insulating film 108 serving as a gate insulating film incontact with the oxide semiconductor film 110, the gate electrode 104overlapping with the oxide semiconductor film 110 and being in contactwith the insulating film 108, and the source electrode 112 a and thedrain electrode 112 b electrically connected to the oxide semiconductorfilm 110.

In addition, over the transistor 150, specifically over the oxidesemiconductor film 110, the source electrode 112 a, and the drainelectrode 112 b, insulating films 114, 116, 118, and 119 are formed. Theinsulating films 114, 116, and 118 function as protective insulatingfilms for the transistor 150. The insulating film 119 functions as aplanarization film. In addition, an opening reaching the drain electrode112 b is formed in the insulating films 114, 116, 118, and 119. Theconductive film 120 is formed over the insulating film 119 to cover theopening. The conductive film 120 has a function of a pixel electrode.Note that a structure without the insulating film 119 may be employed.

The capacitor 160 is provided over the insulating film 116. Thecapacitor 160 includes the oxide semiconductor film 111 serving as theone of the pair of electrodes, the insulating films 118 and 119 servingas dielectric films over the oxide semiconductor film 111, and theconductive film 120 that serves as the other of the pair of electrodesand overlaps with the oxide semiconductor film 111 with the insulatingfilms 118 and 119 provided therebetween. In other words, the conductivefilm 120 serves as the pixel electrode and the electrode of thecapacitor. Note that the oxide semiconductor film 111 preferably has athickness with which a variation in resistivity in the film thicknessdirection is not caused. Specifically, the thickness is preferablygreater than or equal to 30 nm and less than or equal to 70 nm, furtherpreferably greater than or equal to 50 nm and less than or equal to 70nm.

Furthermore, the touch panel 310 illustrated in FIG. 8 includes a touchsensor in the display portion 381. The touch sensor includes, as a pairof electrodes, the oxide semiconductor film 111 and the conductive film334 that is provided over the substrate 372. The transistor 150, thecapacitor 160, and the touch sensor can be collectively referred to as asemiconductor device. Moreover, the transistor 150 and the touch sensorcan also be collectively referred to as a semiconductor device. Notethat as an auxiliary electrode, a conductive film may be formed incontact with the oxide semiconductor film 111. For example, a conductivefilm may be formed in a position overlapping with a light-blocking film332 using a material similar to that of the gate electrode 104 or thatof the source electrode 112 a and the drain electrode 112 b. Since theauxiliary electrode overlaps with the light-blocking film 332, delay ofsignal transmission for detection by the touch sensor can be reducedwhile the aperture ratio of the pixel is maintained.

Note that the oxide semiconductor film 110 serves as a channel region ofthe transistor 150. In addition, the oxide semiconductor film 111 servesas the one of the pair of electrodes of the capacitor 160. Thus, theoxide semiconductor film 111 has resistivity lower than the oxidesemiconductor film 110. In addition, the oxide semiconductor films 110and 111 preferably contain the same metal element. When the oxidesemiconductor films 110 and 111 each contain the same metal element, acommon manufacturing apparatus (e.g., a deposition apparatus or aprocessing apparatus) can be used and accordingly the manufacturing costcan be reduced.

In addition, the capacitor 160 has a light-transmitting property. Inother words, each of the oxide semiconductor film 111, the conductivefilm 120, and the insulating films 118 and 119 that are included in thecapacitor 160 are formed of a material with a light-transmittingproperty. Since the capacitor 160 has a light-transmitting property, thecapacitor 160 can be formed large (in a large area) in the pixel excepta region where the transistor is formed; thus, the touch panel can haveincreased capacitance while improving the aperture ratio. As a result,the touch panel can have an excellent display quality.

Note that as the insulating film 118 over the transistor 150 andincluded in the capacitor 160, an insulating film containing at leasthydrogen is used. In addition, as an insulating film 107 included in thetransistor 150 and the insulating films 114 and 116 over the transistor150, insulating films containing at least oxygen are used. As describedabove, these insulating films are used as the insulating films includedin the transistor 150 and the capacitor 160 and provided over thetransistor 150 and the capacitor 160, so that the resistivity of theoxide semiconductor film 110 included in the transistor 150 and theresistivity of the oxide semiconductor film 111 included in thecapacitor 160 can be controlled.

In addition, when the insulating films included in the capacitor 160 andprovided over the transistor 150 and the capacitor 160 are provided asfollows, the planarity of the conductive film 120 can be increased.Specifically, the insulating films 114 and 116 are formed over the oxidesemiconductor film 110 and the insulating film 118 is formed over theoxide semiconductor film 111 so that the oxide semiconductor film 111 ispositioned between the insulating films 116 and 118, whereby theresistivity of the oxide semiconductor film 111 can be controlledwithout providing an opening in the insulating films 114 and 116 in aposition overlapping with the oxide semiconductor film 111. With such astructure, the orientation of the liquid crystals formed over theconductive film 120 can be favorable.

Note that in FIG. 8, an oxide semiconductor film 111 a is provided tooverlap with the oxide semiconductor film 110. The oxide semiconductorfilm 111 a is formed at the same time using the same deposition step andthe same etching step as the oxide semiconductor film 111. The oxidesemiconductor film 111 a serves as the second gate electrode of thetransistor 150. In that case, the insulating films 114 and 116 serve asgate insulating films for the second gate electrode. In other words, thetransistor 150 includes the insulating films 114 and 116 provided overthe oxide semiconductor film 110, the source electrode 112 a, and thedrain electrode 112 b and the oxide semiconductor film 111 a providedover the insulating films 114 and 116 to overlap with the oxidesemiconductor film 110.

Since the oxide semiconductor film 111 a is formed at the same timeusing the same deposition step and the same etching step as the oxidesemiconductor film 111, an increase in the number of processing stepscan be prevented. Note that one embodiment of the present invention isnot limited to these examples. The oxide semiconductor film 111 a can beformed in a step different from the oxide semiconductor film 111. Theoxide semiconductor film 111 a may be connected to the gate electrode104. Alternatively, the oxide semiconductor film 111 a may be suppliedwith a signal or potential different from the signal or potentialsupplied to the gate electrode 104 without being connected to the gateelectrode 104.

Note that the oxide semiconductor film 110 has higher resistivity thanthe oxide semiconductor film 111 because it is used as the channelregion in the transistor 150. The oxide semiconductor film 111 has lowerresistivity than the oxide semiconductor film 110 because it serves asan electrode. A method of controlling the resistivity of the oxidesemiconductor films 110 and 111 is described later.

The touch panel 310 includes the conductive film 120, the oxidesemiconductor film 111, and the like over the substrate 102. Theconductive film 120, the oxide semiconductor film 111, and/or the likeare included in a transistor 301, the transistor 150, a connectionportion 306, a conductive film 317, and a liquid crystal element 308.

FIG. 8 illustrates the cross section of two pixels as an example of thedisplay portion 381. For example, each of the pixels is a pixelexhibiting a red color, a pixel exhibiting a green color, or a pixelexhibiting a blue color; thus, full-color display can be achieved. Inthe display portion 381 illustrated in FIG. 8, for example, a pixel 388Rincludes the transistor 150, the capacitor 160, the liquid crystalelement 308, and a coloring film 331R. Furthermore, a pixel 388Gincludes a transistor that is not illustrated, the capacitor 160, theliquid crystal element 308, and a coloring film 331G.

FIG. 8 illustrates, as an example of the driver circuit 382, an examplein which the transistor 301 is provided.

FIG. 8 illustrates an example in which the transistors 301 and 150 eachhave a structure in which a semiconductor layer where a channel isformed is provided between two gate electrodes. Such transistors canhave a higher field-effect mobility and thus have a higher on-statecurrent than other transistors. Consequently, a circuit capable ofhigh-speed operation can be obtained. Furthermore, the area occupied bya circuit portion can be reduced. The use of the transistor having ahigh on-state current can reduce signal delay in wirings and cansuppress display unevenness even in a display panel or a touch panel inwhich the number of wirings is increased because of an increase in sizeor resolution.

Note that the transistor 301 included in the driver circuit 382 and thetransistor 150 included in the display portion 381 may have the samestructure. The plurality of transistors included in the driver circuit382 may have the same structure or different structures. The pluralityof transistors included in display portion 381 may have the samestructure or different structures.

In the example illustrated in FIG. 8, a liquid crystal element using afringe field switching (FFS) mode is used as the liquid crystal element308. The liquid crystal element 308 includes the conductive film 120,the liquid crystal 353, and the oxide semiconductor film 111.Orientation of the liquid crystal 353 can be controlled with an electricfield generated between the conductive film 120 and the oxidesemiconductor film 111.

The conductive film 120 has a comb-like top shape or a top shapeprovided with a slit (a top shape is also referred to as a planarshape). The oxide semiconductor film 111 is provided so as to overlapwith the conductive film 120. In a region overlapping with the coloringfilm 331R and the like, there is a portion where the conductive film 120is not provided over the oxide semiconductor film 111.

In FIG. 8, the conductive film 120 functions as a pixel electrode, andthe oxide semiconductor film 111 functions as a common electrode.Alternatively, the conductive film 120 that is provided in an upperlayer and has a comb-like top shape or a top shape provided with a slitmay be used as the common electrode, and the oxide semiconductor film111 that is provided in a lower layer may be used as the pixel electrode(see FIG. 9). In the touch panel 310 illustrated in FIG. 9, the oxidesemiconductor film 111 is electrically connected to the drain electrode112 b of the transistor 150. In this case, the touch sensor in the touchpanel 310 includes the conductive films 334 and 120 as a pair ofelectrodes.

The connection portion 306 is provided in a region near an end portionof the substrate 102. In the connection portion 306, the conductive film317 is electrically connected to the FPC 373 through a connection layer319. In the example illustrated in FIG. 8, the connection portion 306 isformed by stacking part of the conductive film 317 and a conductive filmthat is formed by processing the same conductive film as the conductivefilm 120.

The coloring film 331R, the coloring film 331G, a light-blocking film332, an insulating film 355, and the like are provided on a surface ofthe substrate 372 that is on the substrate 102 side. The conductive film334, the conductive film 335, the conductive film 341, and the like areprovided on the surface of the substrate 372 that is the side oppositeto the substrate 102.

The conductive film 334 is electrically connected to the conductive film341. The conductive film 335 is electrically insulated from theconductive films 334 and 341. The conductive films 334, 341, and 335 arepreferably formed at the same time by processing one conductive film.Alternatively, the conductive films 334 and 341 may be continuous. Inthat case, at least a region that overlaps with the display portion 381corresponds to the conductive film 334 functioning as one electrode ofthe touch sensor, and the other region corresponds to the conductivefilm 341.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 10 is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 310 illustrated in FIG. 8.The dashed-dotted line Z1-Z2 in FIG. 10 corresponds to the displayportion 381 in FIG. 8.

The conductive film 334 that is one electrode of the touch sensorextends in the Y direction. The oxide semiconductor film 111 that is theother electrode of the touch sensor extends in the X direction andintersects with the conductive film 334. The conductive film 335 ispreferably formed using the same conductive film as the conductive film334; however, the conductive film 335 is illustrated with hatching thatis different from that of the conductive film 334 because the functionsof the conductive films 334 and 335 are different. The conductive film335 is brought into an electrically floating state, so that thepotential of one of the conductive film 334 and the oxide semiconductorfilm 111 can be transmitted efficiently to the other via the conductivefilm 335. Accordingly, the sensitivity of the touch sensor can beenhanced.

The coloring films 331R and 331G and the light-blocking film 332 areprovided on the surface of the substrate 372 that is on the substrate102 side (see FIG. 8). The insulating film 355 is provided so as tocover the coloring film 331R and the light-blocking film 332.

The insulating film 355 has a function of an overcoat preventingimpurities contained in the coloring film 331R, the light-blocking film332, and the like from diffusing into the liquid crystal 353.

A spacer 316 is provided over the insulating film 119 to adjust thedistance between the substrate 102 and the substrate 372. Although FIG.8 illustrates the example in which the spacer 316 is in contact withcomponents (e.g., the insulating film 355) on the substrate 372 side,the spacer 316 is not necessarily in contact with them. Moreover, FIG. 8illustrates the example in which the spacer 316 is provided on thesubstrate 102 side; however, the spacer 316 may be provided on thesubstrate 372 side. For example, the spacer 316 can be provided betweenadjacent two sub-pixels. A particulate spacer may be used as the spacer316. Although a material such as silica can be used for the particulatespacer, an elastic material such as an organic resin or rubber ispreferably used. In that case, the particulate spacer may have a shapethat is vertically crushed.

Surfaces of the conductive film 120, the insulating film 119, theinsulating film 355, and the like that are in contact with the liquidcrystal 353 may be provided with alignment films for controlling theorientation of the liquid crystal 353.

At least regions of the conductive films 334 and 335 that overlap withthe coloring film 331R and the like are preferably formed using alight-transmitting material.

In the case where the touch panel 310 includes a transmissive liquidcrystal display device, for example, two polarizing plates that are notillustrated are provided to be above and below the display portion 381.Light from a backlight provided on the outer side of the polarizingplate enters through the polarizing plate. At this time, orientation ofthe liquid crystal 353 is controlled with a voltage applied between theconductive film 120 and the oxide semiconductor film 111. In otherwords, the intensity of light emitted through the polarizing plate canbe controlled. Light entering from the backlight, excluding light in aparticular wavelength range, is absorbed by the coloring film, so thatred, blue, or green light is emitted.

In addition to the polarizing plate, a circularly polarizing plate canbe used, for example. An example of the circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. With the circularly polarizing plate, the viewing angledependency can be reduced.

In the example illustrated here, the liquid crystal element 308 is aliquid crystal element using an FFS mode. However, one embodiment of thepresent invention is not limited thereto, and a liquid crystal elementusing any of a variety of modes can be used. For example, a liquidcrystal element using a vertical alignment (VA) mode, a twisted nematic(TN) mode, an in-plane switching (IPS) mode, an axially symmetricaligned micro-cell (ASM) mode, an optically compensated birefringence(OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, or the like can be used.

Furthermore, a normally black liquid crystal display device, forexample, a transmissive liquid crystal display device using a verticalalignment (VA) mode, may be used as the touch panel 310. Examples of thevertical alignment mode include a multi-domain vertical alignment (MVA)mode, a patterned vertical alignment (PVA) mode, and an advancedsuper-view (ASV) mode.

The liquid crystal element is an element that controls transmission andnon-transmission of light by optical modulation action of the liquidcrystal. Note that optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal (PDLC),ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. Such a liquid crystal material exhibits a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on the conditions.

As the liquid crystal material, either of positive liquid crystal andnegative liquid crystal may be used, and an appropriate liquid crystalmaterial can be used depending on the mode or design to be used.

In the case of employing a horizontal electric field mode, liquidcrystal exhibiting a blue phase for which an alignment film isunnecessary may be used. A blue phase is one of liquid crystal phases,which is generated just before a cholesteric phase changes into anisotropic phase while the temperature of cholesteric liquid crystal isincreased. Since the blue phase appears only in a narrow temperaturerange, a liquid crystal composition in which several weight percent ormore of a chiral material is mixed is used for the liquid crystal layerin order to improve the temperature range. The liquid crystalcomposition that includes liquid crystal exhibiting a blue phase and achiral material has a short response time and has optical isotropy. Inaddition, the liquid crystal composition that includes liquid crystalexhibiting a blue phase and a chiral material does not need alignmenttreatment and has a small viewing angle dependence. An alignment filmdoes not need to be provided and rubbing treatment is thus notnecessary; accordingly, electrostatic discharge damage caused by therubbing treatment can be prevented, and defects and damage of the liquidcrystal display device in the manufacturing process can be reduced.

In this structure example, the touch panel 310 can detect touchoperation or the like by utilizing the capacitance formed between theconductive film 334 and the oxide semiconductor film 111. That is, theoxide semiconductor film 111 serves as one of a pair of electrodes ofthe liquid crystal element 308 as well as one of a pair of electrodes ofthe touch sensor.

A conductive material transmitting visible light is preferably used forthe conductive film 120 and/or the conductive film 334. The conductivefilm 120 and/or the conductive film 334 is formed using, for example, aconductive material containing a metal oxide. For example, a metal oxideamong light-transmitting conductive materials described later can beused.

Alternatively, the conductive film 120 and/or the conductive film 334 ispreferably formed using a metal oxide containing the same metal elementas other conductive films or a semiconductor layer. In particular, inthe case where an oxide semiconductor is used for the semiconductorlayer of the transistor in the touch panel 310, a conductive oxidecontaining a metal element contained in the oxide semiconductor ispreferably used.

A fixed potential is supplied to the conductive film 334; thus,electromagnetic noise from the outside can be blocked. For example, whensensing is not performed, a constant potential that does not influencethe switching of the liquid crystal 353 may be supplied to theconductive film 334. For example, a ground potential, a commonpotential, or a predetermined constant potential can be supplied. Theconductive film 334 and the oxide semiconductor film 111 may be set atthe same potential, for example.

By applying an appropriate potential to the conductive film 334, acomponent in the thickness direction in the directions of an electricfield (the directions of the lines of electric force) generated betweenthe conductive film 120 and the oxide semiconductor film 111 can bereduced, and an electric field can be effectively applied in thedirection substantially perpendicular to the thickness direction (in thelateral direction). Thus, an orientation defect in the liquid crystal353 can be suppressed, and a malfunction such as light leakage can beprevented.

A substrate that an object such as a finger or a stylus directly touchesmay be provided above the conductive films 334 and 335 and the substrate372. In that case, a polarizing plate or a circularly polarizing plateis preferably provided between the substrate 372 and the substrate 102.In that case, the above substrate is preferably provided with aprotective layer (such as a ceramic coat). The protective layer can beformed using an inorganic insulating material such as silicon oxide,aluminum oxide, yttrium oxide, or yttria-stabilized zirconia (YSZ). Inaddition, tempered glass may be used for the above substrate. Thetempered glass that can be used here is one that has been subjected tophysical or chemical treatment by an ion exchange method, a thermaltempering method, or the like and has a surface to which compressivestress has been applied.

[Components]

The above components are described below.

[Substrate]

A substrate having a flat surface can be used as the substrate includedin the touch panel. The substrate through which light emitted from thedisplay element is extracted is formed using a material that transmitsthe light. For example, a material such as glass, quartz, ceramics,sapphire, or an organic resin can be used. Alternatively, a singlecrystal semiconductor substrate or a polycrystalline semiconductorsubstrate made of silicon or silicon carbide, a compound semiconductorsubstrate made of silicon germanium or the like, an SOI substrate, orthe like may be used. Still alternatively, any of these substratesprovided with a semiconductor element may be used as the substrate.

In the case where a glass substrate is used as the substrate, a largeglass substrate having any of the following sizes can be used: the 6thgeneration (1500 mm×1850 mm), the 7th generation (1870 mm×2200 mm), the8th generation (2200 mm×2400 mm), the 9th generation (2400 mm×2800 mm),and the 10th generation (2950 mm×3400 mm). Thus, a large-sized displaydevice can be manufactured. Alternatively, a flexible substrate may beused as the substrate, and a transistor, a capacitor, or the like may beprovided directly over the flexible substrate.

The weight and thickness of the touch panel can be decreased by using athin substrate. Furthermore, a flexible touch panel can be obtained byusing a substrate that is thin enough to have flexibility.

As the glass, for example, non-alkali glass, barium borosilicate glass,aluminoborosilicate glass, or the like can be used.

Examples of a material having flexibility and a light-transmittingproperty with respect to visible light include glass that is thin enoughto have flexibility, polyester resins such as polyethylene terephthalate(PET) and polyethylene naphthalate (PEN), a polyacrylonitrile resin, apolyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC)resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, a polyvinylchloride resin, and a polytetrafluoroethylene (PTFE) resin. Inparticular, a material whose thermal expansion coefficient is low ispreferred, and for example, a polyamide imide resin, a polyimide resin,or PET can be suitably used. A substrate in which a glass fiber isimpregnated with an organic resin or a substrate whose thermal expansioncoefficient is reduced by mixing an organic resin with an inorganicfiller can also be used. A substrate using such a material islightweight, and thus, a touch panel using this substrate can also belightweight.

Since the substrate through which light is not extracted does not needto have a light-transmitting property, a metal substrate using a metalmaterial or an alloy material, a ceramic substrate, a semiconductorsubstrate, or the like can be used as well as the above-describedsubstrates. A metal material and an alloy material, which have highthermal conductivity, are preferable because they can easily conductheat to the whole sealing substrate and accordingly can prevent a localtemperature rise in the touch panel. To obtain flexibility andbendability, the thickness of a metal substrate is preferably greaterthan or equal to 10 μm and less than or equal to 200 μm, more preferablygreater than or equal to 20 μm and less than or equal to 50 μm.

There is no particular limitation on a material of the metal substrate,but it is preferable to use, for example, aluminum, copper, nickel, or ametal alloy such as an aluminum alloy or stainless steel.

It is preferable to use a substrate subjected to insulation treatment insuch a manner that a surface of a conductive substrate is oxidized or aninsulating film is formed on a surface. An insulating film may be formedby, for example, a coating method such as a spin-coating method or adipping method, an electrodeposition method, an evaporation method, or asputtering method. An oxide film may be formed on the substrate surfaceby an anodic oxidation method, exposing to or heating in an oxygenatmosphere, or the like.

The flexible substrate may have a stacked structure of a layer of any ofthe above-mentioned materials and a hard coat layer (e.g., a siliconnitride layer) that protects a surface of the touch panel from damage orthe like, a layer (e.g., an aramid resin layer) that can dispersepressure, or the like. Furthermore, to suppress a decrease in thelifetime of the display element due to moisture and the like, aninsulating film with low water permeability may be provided. Forexample, a film containing nitrogen and silicon (e.g., a silicon nitridefilm or a silicon oxynitride film) or a film containing nitrogen andaluminum (e.g., an aluminum nitride film) may be provided.

The substrate may be formed by stacking a plurality of layers. Inparticular, when a glass layer is used, a barrier property against waterand oxygen can be improved, and thus, a highly reliable touch panel canbe provided.

A substrate in which a glass layer, an adhesive layer, and an organicresin layer are stacked from the side closer to the display element canbe used, for example. The thickness of the glass layer is greater thanor equal to 20 μm and less than or equal to 200 μm, preferably greaterthan or equal to 25 μm and less than or equal to 100 μm. With such athickness, the glass layer can have both a high barrier property againstwater and oxygen and a high flexibility. The thickness of the organicresin layer is greater than or equal to 10 μm and less than or equal to200 μm, preferably greater than or equal to 20 μm and less than or equalto 50 μm. By providing such an organic resin layer, occurrence of abreak or a crack in the glass layer can be inhibited, and the mechanicalstrength can be improved. With the substrate that includes such acomposite material of a glass material and an organic resin, a highlyreliable flexible touch panel can be provided.

[Transistor]

The transistor includes a conductive film functioning as the gateelectrode, the semiconductor layer, a conductive film functioning as thesource electrode, a conductive film functioning as the drain electrode,and the insulating film functioning as the gate insulating film. In theabove example, a bottom-gate transistor is used.

Note that there is no particular limitation on the structure of thetransistor included in the touch panel of one embodiment of the presentinvention. For example, a staggered transistor or an inverted staggeredtransistor may be used. A top-gate transistor or a bottom-gatetransistor may be used.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistor, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

As a semiconductor material for the semiconductor layer of thetransistor, an element of Group 14, a compound semiconductor, or anoxide semiconductor can be used, for example. Typically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anoxide semiconductor containing indium, or the like can be used.

An oxide semiconductor is preferably used as a semiconductor in which achannel of the transistor is formed. In particular, an oxidesemiconductor having a wider band gap than silicon is preferably used. Asemiconductor material having a wider band gap and a lower carrierdensity than silicon is preferably used because the off-state current ofthe transistor can be reduced.

For example, it is preferable that the oxide semiconductor contain atleast indium (In) or zinc (Zn). It is further preferable that the oxidesemiconductor include an In-M-Zn oxide (M is a metal such as Al, Ti, Ga,Ge, Y, Zr, Sn, La, Ce, Sn, or Hf).

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film including a plurality of crystal parts whosec-axes are aligned substantially perpendicular to a surface on which thesemiconductor layer is formed or the top surface of the semiconductorlayer and having no grain boundary between adjacent crystal parts.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film that is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible touch panelthat is used in a bent state, or the like.

Moreover, the use of such an oxide semiconductor for the semiconductorlayer makes it possible to provide a highly reliable transistor in whicha variation in electrical characteristics is suppressed.

Charge accumulated in a capacitor through a transistor can be held for along time because of the low off-state current of the transistor. Whensuch a transistor is used for a pixel, operation of a driver circuit canbe stopped while a gray scale of an image displayed in each displayregion is maintained. As a result, a display device with an extremelylow power consumption can be obtained.

<Oxide Semiconductor Film>

It is preferable that the oxide semiconductor films 110 and 111 eachinclude a film represented by an In-M-Zn oxide that contains, forexample, at least indium (In), zinc (Zn), and M (a metal such as Al, Ti,Ga, Y, Zr, La, Ce, Sn, or Hf). In order to reduce variations inelectrical characteristics of the transistor including the oxidesemiconductor, the oxide semiconductor preferably contains a stabilizerin addition to the above elements.

Examples of the stabilizer, including metals that can be used as M, aregallium (Ga), tin (Sn), hafnium (Hf), aluminum (Al), and zirconium (Zr).Other examples of the stabilizer are lanthanoid such as lanthanum (La),cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium(Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

As an oxide semiconductor included in each of the oxide semiconductorfilms 110 and 111, any of the following oxides can be used, for example:an In—Ga—Zn-based oxide, an In—Al—Zn-based oxide, an In—Sn—Zn-basedoxide, an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, anIn—Ce—Zn-based oxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide,an In—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-basedoxide, an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, anIn—Ho—Zn-based oxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide,an In—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, and anIn—Hf—Al—Zn-based oxide.

Note that here, an “In—Ga—Zn-based oxide” means an oxide containing In,Ga, and Zn as its main components, and there is no limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metalelement in addition to In, Ga, and Zn.

The oxide semiconductor films 110 and 111 may include the same metalelements contained in the above oxides. The use of the same metalelements for the oxide semiconductor films 110 and 111 can reduce themanufacturing cost. For example, when metal oxide targets with the samemetal composition are used, the manufacturing cost can be reduced, andthe same etching gas or the same etchant can be used in processing theoxide semiconductor films 110 and 111. Note that even when the oxidesemiconductor films 110 and 111 include the same metal elements, theyhave different compositions in some cases. For example, a metal elementin a film is released during the manufacturing process of the transistorand the capacitor, which might result in different metal compositions.

Note that in the case where the oxide semiconductor film 110 includes anIn-M-Zn oxide, when the summation of In and M is assumed to be 100atomic %, the atomic proportions of In and M are preferably higher than25 atomic % and lower than 75 atomic %, respectively, more preferablyhigher than 34 atomic % and lower than 66 atomic %, respectively.

The energy gap of the oxide semiconductor film 110 is 2 eV or more,preferably 2.5 eV or more, more preferably 3 eV or more. In this manner,the off-state current of the transistor can be reduced by using an oxidesemiconductor having a wide energy gap.

The thickness of the oxide semiconductor film 110 is greater than orequal to 3 nm and less than or equal to 200 nm, preferably greater thanor equal to 3 nm and less than or equal to 100 nm, more preferablygreater than or equal to 3 nm and less than or equal to 50 nm.

In the case where the oxide semiconductor film 110 includes an In-M-Znoxide (M represents Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, Hf, or Nd), it ispreferable that the atomic ratio of metal elements of a sputteringtarget used for forming a film of the In-M-Zn oxide satisfy In≥M andZn≥M. As the atomic ratio of the metal elements of such a sputteringtarget, In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=1:3:4,In:M:Zn=1:3:6, and the like are given. Note that the atomic ratio ofmetal elements in the formed oxide semiconductor film 110 varies fromthe above atomic ratio of metal elements of the sputtering target withina range of ±40% as an error.

An oxide semiconductor film with a low carrier density is used as theoxide semiconductor film 110. For example, an oxide semiconductor filmwhose carrier density is lower than or equal to 1×10¹⁷/cm³, preferablylower than or equal to 1×10¹⁵/cm³, more preferably lower than or equalto 1×10¹³/cm³, more preferably lower than or equal to 1×10¹¹/cm³ is usedas the oxide semiconductor film 110.

Note that, without limitation to the compositions and materialsdescribed above, a material with an appropriate composition may be useddepending on required semiconductor characteristics and electricalcharacteristics (e.g., field-effect mobility and threshold voltage) ofthe transistor. Furthermore, to obtain required semiconductorcharacteristics of the transistor, it is preferable that the carrierdensity, the impurity concentration, the defect density, the atomicratio of a metal element to oxygen, the interatomic distance, thedensity, and the like of the oxide semiconductor film 110 be set to beappropriate.

When silicon or carbon that is one of elements belonging to Group 14 iscontained in the oxide semiconductor film 110, oxygen vacancies areincreased, and the oxide semiconductor film 110 has n-type conductivity.Thus, the concentration of silicon or carbon (measured by secondary ionmass spectrometry (SIMS)) of the oxide semiconductor film 110 is lowerthan or equal to 2×10¹⁸ atoms/cm³, preferably lower than or equal to2×10¹⁷ atoms/cm³.

Furthermore, the concentration of alkali metal or alkaline earth metalin the oxide semiconductor film 110, which is measured by SIMS, is lowerthan or equal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to2×10¹⁶ atoms/cm³. Alkali metal and alkaline earth metal might generatecarriers when bonded to an oxide semiconductor, in which case theoff-state current of the transistor might be increased. Therefore, it ispreferable to reduce the concentration of alkali metal or alkaline earthmetal in the oxide semiconductor film 110.

When nitrogen is contained in the oxide semiconductor film 110,electrons serving as carriers are generated to increase the carrierdensity, so that the oxide semiconductor film 110 easily has n-typeconductivity. Thus, a transistor including an oxide semiconductor thatcontains nitrogen is likely to be normally on. For this reason, nitrogenin the oxide semiconductor film is preferably reduced as much aspossible; the concentration of nitrogen that is measured by SIMS ispreferably set to, for example, lower than or equal to 5×10¹⁸ atoms/cm³.

The oxide semiconductor film 110 may have a non-single-crystalstructure, for example. The non-single-crystal structure includes ac-axis aligned crystalline oxide semiconductor (CAAC-OS) that isdescribed later, a polycrystalline structure, a microcrystallinestructure that is described later, or an amorphous structure, forexample. Among the non-single-crystal structures, an amorphous structurehas the highest density of defect states, whereas CAAC-OS has the lowestdensity of defect states.

The oxide semiconductor film 110 may have an amorphous structure, forexample. An oxide semiconductor film having an amorphous structure hasdisordered atomic arrangement and no crystalline component, for example.Alternatively, an oxide film having an amorphous structure has, forexample, an absolutely amorphous structure and no crystal part.

Note that the oxide semiconductor film 110 may be a mixed film includingtwo or more of the following: a region having an amorphous structure, aregion having a microcrystalline structure, a region having apolycrystalline structure, a region of CAAC-OS, and a region having asingle-crystal structure. Furthermore, the mixed film has astacked-layer structure of two or more of the following in some cases:the region having an amorphous structure, the region having amicrocrystalline structure, the region having a polycrystallinestructure, the region of CAAC-OS, and the region having a single-crystalstructure.

Note that silicon may be used as a semiconductor in which a channel ofthe transistor is formed. Although amorphous silicon may be used assilicon, silicon having crystallinity is particularly preferable. Forexample, microcrystalline silicon, polycrystalline silicon, singlecrystal silicon, or the like is preferably used. In particular,polycrystalline silicon can be formed at a lower temperature than singlecrystal silicon and has a higher field-effect mobility and a higherreliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are provided at extremelyhigh density, a gate driver circuit and a source driver circuit can beformed over a substrate over which the pixels are formed, and the numberof components of an electronic device can be reduced.

[Conductive Film]

As conductive films such as a gate, a source, and a drain of thetransistor and a wiring and an electrode in the touch panel, asingle-layer structure or a stacked-layer structure using any of metalssuch as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten, or an alloycontaining any of these metals as its main component can be used. Forexample, a single-layer structure of an aluminum film containingsilicon, a two-layer structure in which an aluminum film is stacked overa titanium film, a two-layer structure in which an aluminum film isstacked over a tungsten film, a two-layer structure in which a copperfilm is stacked over a copper-magnesium-aluminum alloy film, a two-layerstructure in which a copper film is stacked over a titanium film, atwo-layer structure in which a copper film is stacked over a tungstenfilm, a three-layer structure in which a titanium film or a titaniumnitride film, an aluminum film or a copper film, and a titanium film ora titanium nitride film are stacked in this order, a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order, and the like can be given. Notethat a transparent conductive material containing indium oxide, tinoxide, or zinc oxide may also be used. Copper containing manganese ispreferably used because controllability of a shape by etching isincreased.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide (ITO), indium zinc oxide, zinc oxide, orzinc oxide to which gallium is added, or graphene can be used.Alternatively, a metal material such as gold, silver, platinum,magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper,palladium, or titanium, or an alloy material containing any of thesemetal materials can be used. Alternatively, a nitride of the metalmaterial (e.g., titanium nitride) or the like may be used. In the caseof using the metal material or the alloy material (or the nitridethereof), the thickness is set small enough to be able to transmitlight. Alternatively, a stack of any of the above materials can be usedas the conductive film. For example, a stacked film of indium tin oxideand an alloy of silver and magnesium is preferably used because theconductivity can be increased.

Alternatively, for the conductive film, an oxide semiconductor similarto that of the semiconductor layer is preferably used. In that case, itis preferable that the conductive film be formed to have a lowerelectric resistance than a region in the semiconductor layer where achannel is formed.

For example, such a conductive film can be used as the oxidesemiconductor films 111 and 111 a. Alternatively, it can be used asanother light-transmitting conductive film.

[Method for Controlling Resistivity of Oxide Semiconductor]

An oxide semiconductor film that can be used as each of the oxidesemiconductor films 110, 111, and 111 a includes a semiconductormaterial whose resistivity can be controlled by oxygen vacancies in thefilm and/or the concentration of impurities such as hydrogen or water inthe film. Thus, treatment to be performed on the oxide semiconductorfilms 110, 111, and 111 a is selected from the following to control theresistivity of each of the oxide semiconductor films: treatment forincreasing oxygen vacancies and/or the impurity concentration andtreatment for reducing oxygen vacancies and/or the impurityconcentration.

Specifically, plasma treatment is performed on the oxide semiconductorfilm used as the oxide semiconductor film 111 serving as the electrodeof the capacitor 160 and the oxide semiconductor film 111 a to increaseoxygen vacancies and/or impurities such as hydrogen or water in theoxide semiconductor film, so that the oxide semiconductor film can havea high carrier density and a low resistivity. Furthermore, an insulatingfilm containing hydrogen is formed in contact with the oxidesemiconductor film to diffuse hydrogen from the insulating filmcontaining hydrogen (e.g., the insulating film 118) to the oxidesemiconductor film, so that the oxide semiconductor film can have a highcarrier density and a low resistivity. As described above, the oxidesemiconductor films 111 and 111 a serve as a semiconductor before thestep of increasing oxygen vacancies or diffusing hydrogen in the films,whereas they serve as a conductor after the step.

Note that in increasing oxygen vacancies in the oxide semiconductor filmby plasma treatment, when the oxide semiconductor film has a largethickness, the degree of an increase in oxygen vacancies is varied inthe oxide semiconductor film in some cases. Moreover, in diffusinghydrogen from the insulating film to the oxide semiconductor film, whenthe oxide semiconductor film has a large thickness, the degree of anincrease in impurities such as hydrogen or water is varied in the oxidesemiconductor film in some cases. As a result, the resistivity of aportion near the bottom surface of the oxide semiconductor film becomeshigher than that of a portion near the top surface of the film in somecases. Thus, with such a variation, even in the case where theresistivity of the oxide semiconductor film is sufficiently low, aconductive film such as a wiring is electrically connected to the oxidesemiconductor film at its bottom surface side, so that contactresistance between the conductive film and the oxide semiconductor filmis increased in some cases. On the other hand, the oxide semiconductorfilm needs to have a thickness that is large enough to serve as aconductive film. Thus, it is preferable that the oxide semiconductorfilms 111 and 111 a each have a thickness with which a variation inresistivity in the film thickness direction is not caused. Specifically,the thickness is preferably 1 than or equal to 30 nm and less than orequal to 70 nm, further preferably greater than or equal to 50 nm andless than or equal to 70 nm.

The oxide semiconductor film 110 that serves as the channel region ofthe transistor 150 is not in contact with an insulating film 106containing hydrogen or the insulating film 118 containing hydrogenbecause the insulating films 107, 114, and 116 are provided. With theuse of an insulating film containing oxygen, in other words, aninsulating film capable of releasing oxygen, for at least one of theinsulating films 107, 114, and 116, oxygen can be supplied to the oxidesemiconductor film 110. The oxide semiconductor film 110 to which oxygenis supplied is an oxide semiconductor film having a high resistivitybecause oxygen vacancies in the film or at the interface arecompensated. Note that as the insulating film capable of releasingoxygen, a silicon oxide film or a silicon oxynitride film can be used,for example.

To reduce the resistivity of the oxide semiconductor film, an ionimplantation method, an ion doping method, a plasma immersion ionimplantation method, or the like can be employed to inject hydrogen,boron, phosphorus, or nitrogen into the oxide semiconductor film.

To reduce the resistivity of the oxide semiconductor film, plasmatreatment may be performed on the oxide semiconductor film. For theplasma treatment, for example, a gas containing at least one of a raregas (He, Ne, Ar, Kr, or Xe), hydrogen, and nitrogen is typically used.Specifically, plasma treatment in an Ar atmosphere, plasma treatment ina mixed gas atmosphere of Ar and hydrogen, plasma treatment in anammonia atmosphere, plasma treatment in a mixed gas atmosphere of Ar andammonia, plasma treatment in a nitrogen atmosphere, or the like can beemployed.

In the oxide semiconductor film subjected to the plasma treatment, anoxygen vacancy is formed in a lattice from which oxygen is released (orin a portion from which oxygen is released). This oxygen vacancy cangenerate a carrier. When hydrogen is supplied from an insulating filmthat is in the vicinity of the oxide semiconductor film, specifically,that is in contact with the lower surface or the upper surface of theoxide semiconductor film, and hydrogen is bonded to the oxygen vacancy,an electron serving as a carrier might be generated.

The oxide semiconductor film in which oxygen vacancies are filled andthe hydrogen concentration is reduced can be referred to as a highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor film. The term “substantially intrinsic” refers to thestate where the oxide semiconductor film has a carrier density of lowerthan 8×10¹¹/cm³, preferably lower than 1×10¹¹/cm³, more preferably lowerthan 1×10¹⁰/cm³. A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has few carrier generationsources and thus can have a low carrier density. The highly purifiedintrinsic or substantially highly purified intrinsic oxide semiconductorfilm has a low density of defect states and accordingly can have a lowdensity of trap states.

The highly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be lower than or equal to themeasurement limit of a semiconductor parameter analyzer, i.e., lowerthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode of from 1 V to 10 V. Accordingly,the transistor 150 in which the channel region is formed in the oxidesemiconductor film 110 formed using a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor film canhave a small variation in electrical characteristics and a highreliability.

For example, an insulating film containing hydrogen, in other words, aninsulating film capable of releasing hydrogen, typically, a siliconnitride film, is used as the insulating film 118, whereby hydrogen canbe supplied to the oxide semiconductor film 111. The hydrogenconcentration in the insulating film capable of releasing hydrogen ispreferably higher than or equal to 1×10²² atoms/cm³. Such an insulatingfilm is formed in contact with the oxide semiconductor films 111 and 111a, whereby hydrogen can be effectively contained in the oxidesemiconductor films 111 and 111 a. In this manner, the resistivity ofthe oxide semiconductor film can be controlled by changing thestructures of the insulating films in contact with the oxidesemiconductor films 110, 111, and 111 a. Note that a material similar tothe insulating film 118 may be used for the insulating film 106. The useof silicon nitride for the insulating film 106 prevents the gateelectrode 104 from being supplied with oxygen diffused from theinsulating film 107 and being oxidized.

Hydrogen contained in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water and also causes an oxygen vacancy ina lattice from which oxygen is released (or a portion from which oxygenis released). Due to entry of hydrogen into the oxygen vacancy, anelectron serving as a carrier is generated in some cases. Furthermore,in some cases, bonding of part of hydrogen to oxygen bonded to a metalatom causes generation of an electron serving as a carrier. Accordingly,the oxide semiconductor film 111 formed in contact with the insulatingfilm containing hydrogen is an oxide semiconductor film that has ahigher carrier density than the oxide semiconductor film 110.

Hydrogen in the oxide semiconductor film 110 of the transistor 150 inwhich a channel region is formed is preferably reduced as much aspossible. Specifically, in the oxide semiconductor film 110, theconcentration of hydrogen that is measured by SIMS is lower than orequal to 2×10²⁰ atoms/cm³, preferably lower than or equal to 5×10¹⁹atoms/cm³, more preferably lower than or equal to 1×10¹⁹ atoms/cm³, morepreferably lower than 5×10¹⁸ atoms/cm³, more preferably lower than orequal to 1×10¹⁸ atoms/cm³, more preferably lower than or equal to 5×10¹⁷atoms/cm³, more preferably lower than or equal to 1×10¹⁶ atoms/cm³.

The oxide semiconductor film 111 serving as the electrode of thecapacitor 160 and the oxide semiconductor film 111 a serving as thesecond gate of the transistor 150 are each an oxide semiconductor filmthat has a higher hydrogen concentration and/or a larger number ofoxygen vacancies than the oxide semiconductor film 110 and has a lowerresistivity than the oxide semiconductor film 110. The hydrogenconcentration in the oxide semiconductor films 111 and 111 a is higherthan or equal to 8×10¹⁹ atoms/cm³, preferably higher than or equal to1×10²⁰ atoms/cm³, more preferably higher than or equal to 5×10²⁰atoms/cm³. The hydrogen concentration in the oxide semiconductor films111 and 111 a is greater than or equal to 2 times, preferably greaterthan or equal to 10 times the hydrogen concentration in the oxidesemiconductor film 110. The resistivity of the oxide semiconductor films111 and 111 a is preferably greater than or equal to 1×10⁻⁸ times andless than 1×10⁻¹ times the resistivity of the oxide semiconductor film110. The resistivity of the conductive film is typically higher than orequal to 1×10⁻³ Ωcm and lower than 1×10⁴ Ωcm, preferably higher than orequal to 1×10⁻³ Ωcm and lower than 1×10⁻¹ Ωcm.

<Insulating Film>

As each of the insulating films 106 and 107 serving as a gate insulatingfilm of the transistor 150, an insulating film including at least one ofthe following films formed by a plasma chemical vapor deposition (CVD)method, a sputtering method, or the like can be used: a silicon oxidefilm, a silicon oxynitride film, a silicon nitride oxide film, a siliconnitride film, an aluminum oxide film, a hafnium oxide film, an yttriumoxide film, a zirconium oxide film, a gallium oxide film, a tantalumoxide film, a magnesium oxide film, a lanthanum oxide film, a ceriumoxide film, and a neodymium oxide film. Note that the stacked structureof the insulating films 106 and 107 is not necessarily employed, and aninsulating film with a single-layer structure selected from the abovefilms may be used.

The insulating film 106 has a function of a blocking film that inhibitspenetration of oxygen. For example, in the case where excess oxygen issupplied to the insulating film 107, the insulating film 114, theinsulating film 116, and/or the oxide semiconductor film 110, theinsulating film 106 can inhibit penetration of oxygen.

Note that the insulating film 107 that is in contact with the oxidesemiconductor film 110 serving as a channel region of the transistor 150is preferably an oxide insulating film and preferably includes a regionincluding oxygen in excess of the stoichiometric composition (anoxygen-excess region). In other words, the insulating film 107 is aninsulating film that is capable of releasing oxygen. In order to providethe oxygen-excess region in the insulating film 107, the insulating film107 is formed in an oxygen atmosphere, for example. Alternatively, theoxygen-excess region may be formed by supplying oxygen to the formedinsulating film 107. As a method for supplying oxygen, an ionimplantation method, an ion doping method, a plasma immersion ionimplantation method, plasma treatment, or the like can be employed.

In the case where hafnium oxide is used for the insulating films 106 and107, the following effect is attained. Hafnium oxide has a higherdielectric constant than silicon oxide and silicon oxynitride.Therefore, the thicknesses of the insulating films 106 and 107 can bemade large as compared with the case where silicon oxide is used; as aresult, a leakage current due to a tunnel current can be low. That is,it is possible to provide a transistor with a low off-state current.Moreover, hafnium oxide with a crystalline structure has higherdielectric constant than hafnium oxide with an amorphous structure.Therefore, it is preferable to use hafnium oxide with a crystallinestructure in order to provide a transistor with a low off-state current.Examples of the crystalline structure include a monoclinic crystalstructure and a cubic crystal structure. Note that one embodiment of thepresent invention is not limited to the above examples.

In this embodiment, a silicon nitride film is formed as the insulatingfilm 106, and a silicon oxide film is formed as the insulating film 107.The silicon nitride film has a higher dielectric constant than a siliconoxide film and needs a larger thickness for capacitance equivalent tothat of the silicon oxide film. Thus, when the silicon nitride film isincluded as the insulating film 108 serving as the gate insulating filmof the transistor 150, the physical thickness of the insulating film canbe increased. Therefore, the electrostatic breakdown of the transistor150 can be prevented by inhibiting a reduction in the withstand voltageof the transistor 150 and improving the withstand voltage of thetransistor 150.

<Protective Insulating Film>

As each of the insulating films 114, 116, and 118 serving as aprotective insulating film of the transistor 150, an insulating filmincluding at least one of the following films formed by a plasma CVDmethod, a sputtering method, or the like can be used: a silicon oxidefilm, a silicon oxynitride film, a silicon nitride oxide film, a siliconnitride film, an aluminum oxide film, a hafnium oxide film, an yttriumoxide film, a zirconium oxide film, a gallium oxide film, a tantalumoxide film, a magnesium oxide film, a lanthanum oxide film, a ceriumoxide film, and a neodymium oxide film.

Note that the insulating film 114 that is in contact with the oxidesemiconductor film 110 serving as a channel region of the transistor 150is preferably an oxide insulating film capable of releasing oxygen. Inother words, the insulating film capable of releasing oxygen is aninsulating film that includes a region containing oxygen in excess ofthat in the stoichiometric composition (oxygen-excess region). In orderto provide the oxygen-excess region in the insulating film 114, theinsulating film 114 is formed in an oxygen atmosphere, for example.Alternatively, the oxygen-excess region may be formed by supplyingoxygen to the formed insulating film 114. As a method for supplyingoxygen, an ion implantation method, an ion doping method, a plasmaimmersion ion implantation method, plasma treatment, or the like can beemployed.

The use of the insulating film capable of releasing oxygen as theinsulating film 114 can reduce the number of oxygen vacancies in theoxide semiconductor film 110 by transferring oxygen to the oxidesemiconductor film 110 serving as the channel region of the transistor150. For example, the number of oxygen vacancies in the oxidesemiconductor film 110 can be reduced by using an insulating film havingthe following feature: the number of oxygen molecules released from theinsulating film by heat treatment at a temperature higher than or equalto 100° C. and lower than or equal to 700° C., or higher than or equalto 100° C. and lower than or equal to 500° C. is greater than or equalto 1.0×10¹⁸ molecules/cm³ when measured by thermal desorptionspectroscopy (hereinafter referred to as TDS).

It is preferable that the number of defects in the insulating film 114be small, typically the spin density corresponding to a signal thatappears at g=2.001 due to a dangling bond of silicon be lower than orequal to 3×10¹⁷ spins/cm³ by ESR measurement. This is because if thedensity of defects in the insulating film 114 is high, oxygen is bondedto the defects and the amount of oxygen that permeates the insulatingfilm 114 is decreased. Furthermore, it is preferable that the amount ofdefects at the interface between the insulating film 114 and the oxidesemiconductor film 110 be small and typically, the spin density of asignal that appears at g=1.89 or more and 1.96 or less due to the defectin the oxide semiconductor film 110 be lower than or equal to 1×10¹⁷spins/cm³, more preferably lower than or equal to the lower limit ofdetection by ESR measurement.

Note that all oxygen entering the insulating film 114 from the outsidemoves to the outside of the insulating film 114 in some cases.Alternatively, some oxygen entering the insulating film 114 from theoutside remains in the insulating film 114 in some cases. Furthermore,movement of oxygen occurs in the insulating film 114 in some cases insuch a manner that oxygen enters the insulating film 114 from theoutside and oxygen contained in the insulating film 114 moves to theoutside of the insulating film 114. When an oxide insulating film thatis permeable to oxygen is formed as the insulating film 114, oxygenreleased from the insulating film 116 provided over the insulating film114 can be moved to the oxide semiconductor film 110 through theinsulating film 114.

The insulating film 114 can be formed using an oxide insulating filmhaving a low density of states due to nitrogen oxide. Note that thedensity of states due to nitrogen oxide can be formed between the energyof the valence band maximum (E_(v) _(_) _(os)) and the energy of theconduction band minimum (E_(c) _(_) _(os)) of the oxide semiconductorfilm. A silicon oxynitride film that releases less nitrogen oxide, analuminum oxynitride film that releases less nitrogen oxide, or the likecan be used as the oxide insulating film.

Note that a silicon oxynitride film that releases a small amount ofnitrogen oxide is a film of which the amount of released ammonia islarger than the amount of released nitrogen oxide in TDS; the amount ofreleased ammonia is typically greater than or equal to 1×10¹⁸molecules/cm³ and less than or equal to 5×10¹⁹ molecules/cm³. The amountof released ammonia corresponds to the released amount caused by heattreatment at a film surface temperature higher than or equal to 50° C.and lower than or equal to 650° C., preferably higher than or equal to50° C. and lower than or equal to 550° C.

Nitrogen oxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2),typically NO₂ or NO, forms levels in the insulating film 114, forexample. The levels are positioned in the energy gap of the oxidesemiconductor film 110. Therefore, when nitrogen oxide is diffused tothe interface between the insulating film 114 and the oxidesemiconductor film 110, an electron is trapped by the level on theinsulating film 114 side. As a result, the trapped electron remains inthe vicinity of the interface between the insulating film 114 and theoxide semiconductor film 110; thus, the threshold voltage of thetransistor is shifted in the positive direction.

Nitrogen oxide reacts with ammonia and oxygen in heat treatment. Sincenitrogen oxide contained in the insulating film 114 reacts with ammoniacontained in the insulating film 216 in heat treatment, nitrogen oxidecontained in the insulating film 114 is reduced. Therefore, an electronis hardly trapped at the interface between the insulating film 114 andthe oxide semiconductor film 110.

In a transistor using the oxide insulating film as the insulating film114, the shift in threshold voltage can be reduced, which leads to asmaller change in electrical characteristics of the transistor.

Note that in an ESR spectrum obtained at 100 K or lower of theinsulating film 114, by heat treatment in a manufacturing process of thetransistor, typically heat treatment at a temperature lower than 400° C.or lower than 375° C. (preferably higher than or equal to 340° C. andlower than or equal to 360° C.), a first signal that appears at ag-factor of greater than or equal to 2.037 and less than or equal to2.039, a second signal that appears at a g-factor of greater than orequal to 2.001 and less than or equal to 2.003, and a third signal thatappears at a g-factor of greater than or equal to 1.964 and less than orequal to 1.966 are observed. The split width of the first and secondsignals and the split width of the second and third signals, which areobtained by ESR measurement using an X-band, are each approximately 5mT. The sum of the spin densities of the first signal that appears at ag-factor of greater than or equal to 2.037 and less than or equal to2.039, the second signal that appears at a g-factor of greater than orequal to 2.001 and less than or equal to 2.003, and the third signalthat appears at a g-factor of greater than or equal to 1.964 and lessthan or equal to 1.966 is less than 1×10¹⁸ spins/cm³, typically greaterthan or equal to 1×10¹⁷ spins/cm³ and less than 1×10¹⁸ spins/cm³.

In the ESR spectrum at 100 K or lower, the first signal that appears ata g-factor of greater than or equal to 2.037 and less than or equal to2.039, the second signal that appears at a g-factor of greater than orequal to 2.001 and less than or equal to 2.003, and the third signalthat appears at a g-factor of greater than or equal to 1.964 and lessthan or equal to 1.966 correspond to signals attributed to nitrogenoxide (NO_(x); x is greater than 0 and less than or equal to 2,preferably greater than or equal to 1 and less than or equal to 2).Typical examples of nitrogen oxide include nitrogen monoxide andnitrogen dioxide. In other words, the smaller the sum of the spindensities of the first signal that appears at a g-factor greater than orequal to 2.037 and less than or equal to 2.039, the second signal thatappears at a g-factor greater than or equal to 2.001 and less than orequal to 2.003, and the third signal that appears at a g-factor greaterthan or equal to 1.964 and less than or equal to 1.966 is, the lower thecontent of nitrogen oxide in the oxide insulating film is.

The nitrogen concentration of the oxide insulating film measured by SIMSis lower than or equal to 6×10²⁰ atoms/cm³.

The oxide insulating film is formed by a PECVD method at a substratetemperature higher than or equal to 220° C. and lower than or equal to350° C. using silane and dinitrogen monoxide, whereby a dense and hardfilm can be formed.

The insulating film 116 in contact with the insulating film 114 isformed using an oxide insulating film whose oxygen content is in excessof that in the stoichiometric composition. Part of oxygen is releasedfrom the oxide insulating film whose oxygen content is in excess of thatin the stoichiometric composition by heating. The oxide insulating filmwhose oxygen content is in excess of that in the stoichiometriccomposition is an oxide insulating film of which the amount of releasedoxygen converted into oxygen atoms is greater than or equal to 1.0×10¹⁹atoms/cm³, preferably greater than or equal to 3.0×10²⁰ atoms/cm³ inTDS. Note that the temperature of the film surface in the TDS ispreferably higher than or equal to 100° C. and lower than or equal to700° C., or higher than or equal to 100° C. and lower than or equal to500° C.

Furthermore, it is preferable that the amount of defects in theinsulating film 116 be small, typically the spin density of a signalthat appears at g=2.001 due to a dangling bond of silicon be less than1.5×10¹⁸ spins/cm³, preferably less than or equal to 1×10¹⁸ spins/cm³ byESR measurement. Note that the insulating film 116 is provided moreapart from the oxide semiconductor film 110 than the insulating film 114is; thus, the insulating film 116 may have higher defect density thanthe insulating film 114.

The thickness of the insulating film 114 can be greater than or equal to5 nm and less than or equal to 150 nm, preferably greater than or equalto 5 nm and less than or equal to 50 nm, more preferably greater than orequal to 10 nm and less than or equal to 30 nm. The thickness of theinsulating film 116 can be greater than or equal to 30 nm and less thanor equal to 500 nm, preferably greater than or equal to 150 nm and lessthan or equal to 400 nm.

The insulating films 114 and 116 can be formed using insulating filmsformed of the same kinds of materials; thus, a boundary between theinsulating films 114 and 116 cannot be clearly observed in some cases.Thus, in this embodiment, the boundary between the insulating films 114and 116 is shown by a dashed line. Although a two-layer structure of theinsulating films 114 and 116 is described in this embodiment, thepresent invention is not limited to this. For example, a single-layerstructure of the insulating film 114, a single-layer structure of theinsulating film 116, or a stacked-layer structure of three or morelayers may be used.

The insulating film 118 serving as a dielectric film of the capacitor160 is preferably a nitride insulating film. The relative dielectricconstant of a silicon nitride film is higher than that of a siliconoxide film, and the silicon nitride film needs to have a larger filmthickness than the silicon oxide film to obtain a capacitance equivalentto that of the silicon oxide film. Thus, when the silicon nitride filmis included in the insulating film 118 serving as the dielectric film ofthe capacitor 160, the physical thickness of the insulating film can beincreased. Accordingly, a reduction in the withstand voltage of thecapacitor 160 can be inhibited. Furthermore, the electrostatic breakdownof the capacitor 160 can be prevented by improving the withstandvoltage. Note that the insulating film 118 also has a function ofdecreasing the resistivity of the oxide semiconductor film 111 thatfunctions as the electrode of the capacitor 160.

The insulating film 118 has a function of blocking oxygen, hydrogen,water, an alkali metal, an alkaline earth metal, or the like. Byproviding the insulating film 118, it is possible to prevent outwarddiffusion of oxygen from the oxide semiconductor film 110, outwarddiffusion of oxygen contained in the insulating films 114 and 116, andentry of hydrogen, water, or the like into the oxide semiconductor film110 from the outside. Note that instead of the nitride insulating filmhaving a blocking effect against oxygen, hydrogen, water, an alkalimetal, an alkaline earth metal, and the like, an oxide insulating filmhaving a blocking effect against oxygen, hydrogen, water, and the like,may be provided. As the oxide insulating film having a blocking effectagainst oxygen, hydrogen, water, and the like, an aluminum oxide film,an aluminum oxynitride film, a gallium oxide film, a gallium oxynitridefilm, an yttrium oxide film, an yttrium oxynitride film, a hafnium oxidefilm, and a hafnium oxynitride film can be given.

Examples of an insulating material that can be used for a planarizationfilm, an overcoat, a spacer, and the like include a resin such as anacrylic resin or an epoxy resin, a resin having a siloxane bond, and aninorganic insulating material such as silicon oxide, silicon oxynitride,silicon nitride oxide, silicon nitride, or aluminum oxide.

[Adhesive Layer]

For the adhesive layer, a curable resin such as a heat curable resin, aphotocurable resin, or a two-component type curable resin can be used.For instance, an acrylic resin, polyurethane, an epoxy resin, or a resinhaving a siloxane bond can be used.

[Connection Layer]

For the connection layer, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

[Coloring Film]

Examples of a material that can be used for the coloring film include ametal material, a resin material, and a resin material containing apigment or dye.

The above is the description of the components.

[Cross-Sectional Structure Example 2]

FIG. 11 illustrates a structure example of a cross section of a touchpanel that is partly different from the above-described structureexamples. Note that the description of the portions already described isomitted and different portions are described.

FIG. 11 has a structure in which the conductive films 334, 335, and 341and the FPC 375 are not provided on the display surface side of thesubstrate 372. The oxide semiconductor film 111 serving as a commonelectrode of the liquid crystal element 308 also serves as the pair ofelectrodes of the touch sensor. Specifically, an oxide semiconductorfilm 111 b that extends in one direction and an oxide semiconductor film111 c that is electrically connected to a conductive film 104 aextending in the direction orthogonal to the oxide semiconductor film111 b serve as the pair of electrodes of the touch sensor. With such astructure, the processing steps can be simpler than those of thestructure illustrated in FIG. 8. Note that the oxide semiconductor film111 c is electrically connected to the conductive film 104 a via anopening 333 provided in the insulating films 108, 114, and 116. Theconductive film 104 a can be formed at the same time using the samematerial as the gate electrode 104.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 12A is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 310 illustrated in FIG. 11.The dashed-dotted line Z3-Z4 in FIG. 12A corresponds to the displayportion 381 in FIG. 11.

The oxide semiconductor film 111 b that is one electrode of the touchsensor extends in the Y direction. The oxide semiconductor film 111 cthat is the other electrode of the touch sensor is electricallyconnected to the conductive film 104 a via the opening 333. Theconductive film 104 a extends in the X direction and intersects with theoxide semiconductor film 111 b.

Alternatively, as the conductive film extending in one direction, aconductive film 112 that is formed at the same time using the samematerial as the source electrode 112 a and the drain electrode 112 b maybe used instead of the conductive film 104 a (see FIG. 12B). Note thatFIG. 12B shows an example in which the oxide semiconductor film 111 bextends in the X direction and the conductive film 112 extends in the Ydirection. The oxide semiconductor film 111 c is electrically connectedto the conductive film 112 via an opening 336 provided in the insulatingfilm 118 (not illustrated).

Other Examples

Note that one embodiment of the present invention is not limited to theabove-described structures and can have various structures.

<Peripheral Circuit>

A peripheral circuit can be formed outside a substrate over which pixelsare formed. That is, a circuit for driving a touch sensor and a circuitfor driving a pixel can be separately formed. Note that one circuit canalso have both the functions.

A driver circuit for selecting one of the conductive films (electrodes)in the X direction or one of the conductive films (electrodes) in the Ydirection of the touch sensor can be formed with a TFT over a substrateover which pixels are formed.

The circuit for driving a touch sensor may be provided on the gatedriver side for driving a pixel or the source driver side.

An IC is preferably used as a circuit that has a sensing function and isone of two circuits, a circuit electrically connected to the conductivefilms (electrodes) in the X direction and a circuit electricallyconnected to the conductive films (electrodes) in the Y direction, ofthe touch sensor. In that case, the conductive films are preferablycontrolled with the IC via an FPC.

<Material for Conductive Film (Electrode) of Touch Sensor>

The pair of conductive films of the touch sensor is preferably formedusing the same material as the common electrode, the pixel electrode, orthe like of the liquid crystal element.

Alternatively, the pair of conductive films of the touch sensor may beformed of a meshed metal film (also referred to as a metal mesh).

By providing a metal film directly on or below at least one of theconductive film (electrode) in the X direction and the conductive film(electrode) in the Y direction of the touch sensor, the resistance ofthe conductive film can be reduced. In that case, a stacked structure ofa conductive film including a metal oxide and a conductive filmincluding a metal is preferably used, because these conductive films canbe formed by a patterning technique using a half tone mask and thus theprocess can be simplified.

<Wiring for Connecting Conductive Films (Electrodes) of Touch Sensor>

In a region of the touch sensor where the conductive film in the Xdirection intersects with the conductive film in the Y direction, abridge structure using another conductive film is formed in such amanner that, for example, by using a conductive film on the same planeas the gate electrode of the transistor, conductive films in the Xdirection are provided in the lateral direction parallel to the gateline throughout the pixels. Alternatively, by using a conductive film onthe same plane as the source electrode and the drain electrode of thetransistor, the conductive films in the Y direction are provided in thevertical direction parallel to the source line throughout the pixels. Inthat case, a contact portion is formed in the pixel. Alternatively, thesame conductive film as the conductive film functioning as the commonelectrode or a conductive film on the same plane as the conductive filmfunctioning as the pixel electrode may also be used.

<Conductive Film (Electrode) of Touch Sensor and Conductive Film(Electrode) of Liquid Crystal Element>

A conductive film (electrode) having a slit on the upper side and can beused as the pixel electrode, and a conductive film (electrode) providedacross a plurality of pixels on the lower side can be used as the commonelectrode.

Alternatively, a conductive film (electrode) that is provided across aplurality of pixels on the upper side and has a slit can be used as thecommon electrode, and a conductive film (electrode) that is provided onthe lower side can be used as the pixel electrode.

The conductive film in the X direction of the touch sensor can alsoserve as the conductive film functioning as the pixel electrode or theconductive film functioning as the common electrode.

Alternatively, the conductive film in the Y direction of the touchsensor can also serve as the conductive film functioning as the pixelelectrode or the conductive film functioning as the common electrode.

In addition, the conductive film in the X direction of the touch sensormay be one of a conductive film to which a pulse voltage is applied anda conductive film for sensing a current. In that case, the conductivefilm in the Y direction of the touch sensor may be the other of theconductive films.

The conductive film functioning as the common electrode may be providedacross a plurality of pixels. For example, the conductive filmfunctioning as the common electrode may be electrically connected to acommon wiring formed using a conductive film on the same plane as thegate electrode of the transistor. In that case, one conductive filmfunctioning as the common electrode may have an island-shape.

<Counter Substrate>

When a substrate (also referred to as a counter substrate) that facesthe substrate provided with the transistor and the like is provided withthe conductive film in the X direction or the conductive film in the Ydirection of the touch sensor, a light-blocking film is preferablyprovided closer to the viewing side than the conductive film.

In the case where the counter substrate is provided with one electrodeof a liquid crystal element using a TN mode, an MVA mode, or the like,the one electrode may have a slit in a region that overlaps with theconductive film of the touch sensor provided on the counter substrate.

In the case where a pair of electrodes of a liquid crystal element areprovided over a substrate over which a transistor and the like areprovided as in the case of a liquid crystal element using an FFS mode,an IPS mode, or the like, the counter substrate may be provided with aconductive film for controlling the orientation of liquid crystal. In amanner similar to the above, the conductive film for controlling theorientation of liquid crystal may also have a slit in a region thatoverlaps with the conductive film of the touch sensor.

<Driving Method>

As a method for driving the touch sensor, for example, a method in whichsensing (scanning) of the corresponding row is performed in a periodbetween horizontal periods (gate selection periods) for the driving ofthe pixel can be used. Alternatively, one frame period may be divided intwo periods; writing to all pixels may be performed in the formerperiod, and sensing may be performed in the latter period.

<Method for Manufacturing Transistor, Capacitor, and the Like>

Next, an example of a method for manufacturing the transistor 150 and apair of electrodes included in the capacitor 160 and the liquid crystalelement 308 (the oxide semiconductor film 111 and the conductive film120) in the touch panel 310 illustrated in FIG. 8 is described withreference to FIGS. 25A to 25D, FIGS. 26A to 26C, FIGS. 27A to 27C, andFIG. 28.

First, the gate electrode 104 is formed over the substrate 102. Afterthat, the insulating film 108 including the insulating films 106 and 107is formed over the substrate 102 and the gate electrode 104 (see FIG.25A).

Note that the substrate 102, the gate electrode 104, and the insulatingfilms 106 and 107 can be selected from the materials that are describedabove. In this embodiment, a glass substrate is used as the substrate102; a tungsten film is used as a conductive film for the gate electrode104; a silicon nitride film releasing hydrogen is used as the insulatingfilm 106; and a silicon oxynitride film releasing oxygen is used as theinsulating film 107.

To form the gate electrode 104, a conductive film is formed over thesubstrate 102, is patterned so that a desired region thereof remains,and unnecessary regions are etched.

Next, the oxide semiconductor film 110 is formed in a region overlappingwith the gate electrode 104 over the insulating film 108 (see FIG. 25B).

The oxide semiconductor film 110 can be formed using any of thematerials described above. In this embodiment, as the oxidesemiconductor film 110, an In—Ga—Zn oxide film, which is formed using ametal oxide target with In:Ga:Zn=1:1:1.2 [atomic ratio], is used.

The oxide semiconductor film 110 can be formed in such a manner that anoxide semiconductor film is formed over the insulating film 108, theoxide semiconductor film is patterned so that a desired region thereofremains, and then unnecessary regions are etched.

After formation of the oxide semiconductor film 110, heat treatment ispreferably performed. The heat treatment is preferably performed at atemperature of higher than or equal to 250° C. and lower than or equalto 650° C., preferably higher than or equal to 300° C. and lower than orequal to 500° C., more preferably higher than or equal to 350° C. andlower than or equal to 450° C., in an inert gas atmosphere, anatmosphere containing an oxidizing gas at 10 ppm or more, or a reducedpressure atmosphere. Alternatively, the heat treatment may be performedfirst in an inert gas atmosphere, and then another heat treatment isperformed in an atmosphere containing an oxidizing gas at 10 ppm or morein order to compensate oxygen released from the oxide semiconductor film110. By this heat treatment, impurities such as hydrogen and water canbe removed from at least one of the insulating film 106, the insulatingfilm 107, and the oxide semiconductor film 110. Note that theabove-described heat treatment may be performed before the oxidesemiconductor film 110 is processed into an island shape.

Note that stable electrical characteristics can be effectively impartedto the transistor 150 in which the oxide semiconductor film 110 servesas a channel region by reducing the concentration of impurities in theoxide semiconductor film 110 to make the oxide semiconductor film 110intrinsic or substantially intrinsic.

Next, a conductive film is formed over the insulating film 108 and theoxide semiconductor film 110 and is patterned so that a desired regionthereof remains and unnecessary regions are etched, whereby the sourceelectrode 112 a and the drain electrode 112 b are formed over theinsulating film 108 and the oxide semiconductor film 110 (see FIG. 25C).

The source electrode 112 a and the drain electrode 112 b can be formedusing a material selected from the above-described materials. Note thatin this embodiment, a three-layered structure including a tungsten film,an aluminum film, and a titanium film can be used for the sourceelectrode 112 a and the drain electrode 112 b.

After the source electrode 112 a and the drain electrode 112 b areformed, a surface of the oxide semiconductor film 110 may be cleaned.The cleaning may be performed, for example, using a chemical solutionsuch as phosphoric acid. The cleaning using a chemical solution such asa phosphoric acid can remove impurities (e.g., elements contained in thesource electrode 112 a and the drain electrode 112 b) attached to thesurface of the oxide semiconductor film 110. Note that the cleaning isnot necessarily performed, and thus the cleaning may be unnecessary.

In addition, in the step of forming the source electrode 112 a and thedrain electrode 112 b and/or the cleaning step, the thickness of aregion of the oxide semiconductor film 110 that is not covered by thesource electrode 112 a and the drain electrode 112 b might be reduced.

Next, the insulating films 114 and 116 are formed over the insulatingfilm 108, the oxide semiconductor film 110, the source electrode 112 a,and the drain electrode 112 b. Then, the insulating films 114 and 116are patterned so that a desired region thereof remains and unnecessaryregions are etched, whereby an opening 141 is formed (see FIG. 25D).

Note that after the insulating film 114 is formed, the insulating film116 is preferably formed in succession without exposure to the air.After the insulating film 114 is formed, the insulating film 116 isformed in succession by adjusting at least one of the flow rate of asource gas, pressure, a high-frequency power, and a substratetemperature without exposure to the air, whereby the concentration ofimpurities attributed to the atmospheric component at the interfacebetween the insulating film 114 and the insulating film 116 can bereduced, and oxygen in the insulating films 114 and 116 can be moved tothe oxide semiconductor film 110; accordingly, the amount of oxygenvacancy in the oxide semiconductor film 110 can be reduced.

Note that the insulating film 114 functions as a protective film for theoxide semiconductor film 110 in the step of forming the insulating film116. Consequently, the insulating film 116 can be formed using thehigh-frequency power having a high power density while damage to theoxide semiconductor film 110 is reduced.

The insulating films 114 and 116 can be formed using any of thematerials described above. In this embodiment, a silicon oxynitride filmcapable of releasing oxygen is used as the insulating films 114 and 116.

Heat treatment (hereinafter referred to as first heat treatment) ispreferably performed after the insulating films 114 and 116 are formed.The first heat treatment can reduce nitrogen oxide included in theinsulating films 114 and 116. By the first heat treatment, part ofoxygen included in the insulating films 114 and 116 can be moved to theoxide semiconductor film 110, so that the amount of oxygen vacancyincluded in the oxide semiconductor film 110 can be reduced.

The temperature of the first heat treatment is typically lower than 400°C., preferably lower than 375° C., further preferably higher than orequal to 150° C. and lower than or equal to 350° C. The first heattreatment may be performed under an atmosphere of nitrogen, oxygen,ultra-dry air (air with a water content of 20 ppm or less, preferably 1ppm or less, more preferably 10 ppb or less), or a rare gas (argon,helium, or the like). The atmosphere of nitrogen, oxygen, ultra-dry air,or a rare gas preferably does not contain hydrogen, water, and the like.An electric furnace, a rapid thermal annealing (RTA) apparatus, or thelike can be used for the heat treatment.

The opening 141 is formed to expose part of the drain electrode 112 b.The opening 141 can be formed by a dry etching method, for example.Alternatively, a wet etching method or a combination of dry etching andwet etching can be employed for formation of the opening 141. Note thatthe etching step of forming the opening 141 can reduce the thickness ofthe drain electrode 112 b in some cases.

Next, an oxide semiconductor film to be the oxide semiconductor films111 and 111 a is formed over the insulating film 116 to cover theopening 141 (see FIGS. 26A and 26B).

Note that FIG. 26A is a schematic cross-sectional view of the inside ofa deposition apparatus when the oxide semiconductor film is formed overthe insulating film 116. In FIG. 26A, a sputtering apparatus is used asthe deposition apparatus, and a target 193 placed inside the sputteringapparatus and plasma 194 formed under the target 193 are schematicallyshown.

When the oxide semiconductor film is formed, plasma discharge isperformed in an atmosphere containing an oxygen gas. At this time,oxygen is added to the insulating film 116 over which the oxidesemiconductor film is to be formed. When the oxide semiconductor film isformed, an inert gas (e.g., a helium gas, an argon gas, or a xenon gas)and the oxygen gas may be mixed. For example, it is preferable to usethe argon gas and the oxygen gas with the flow rate of the oxygen gashigher than the flow rate of the argon gas. When the flow rate of theoxygen gas is set higher, oxygen can be favorably added to theinsulating film 116. As an example of the formation conditions of theoxide semiconductor film, the proportion of the oxygen gas in a wholedeposition gas is higher than or equal to 50% and lower than or equal to100%, preferably higher than or equal to 80% and lower than or equal to100%.

In FIG. 26A, oxygen or excess oxygen added to the insulating film 116 isschematically shown by arrows of broken lines.

The oxide semiconductor film is formed at a substrate temperature higherthan or equal to room temperature and lower than 340° C., preferablyhigher than or equal to room temperature and lower than or equal to 300°C., further preferably higher than or equal to 100° C. and lower than orequal to 250° C., still further preferably higher than or equal to 100°C. and lower than or equal to 200° C. The oxide semiconductor film isformed while being heated, so that the crystallinity of the oxidesemiconductor film can be increased. On the other hand, in the casewhere a large-sized glass substrate (e.g., the 6th generation to the10th generation) is used as the substrate 102 and the oxidesemiconductor film is formed at a substrate temperature higher than orequal to 150° C. and lower than 340° C., the substrate 102 might bechanged in shape (distorted or warped). In the case where a large-sizedglass substrate is used, the change in the shape of the glass substratecan be suppressed by forming the oxide semiconductor film at a substratetemperature higher than or equal to 100° C. and lower than 150° C.

The oxide semiconductor film can be formed using any of the materialsdescribed above. In this embodiment, the oxide semiconductor film isformed by a sputtering method using an In—Ga—Zn metal oxide target (withIn:Ga:Zn=1:3:6 [atomic ratio]).

Next, the oxide semiconductor film is processed into a desired shape toform the island-shaped oxide semiconductor films 111 and 111 a (see FIG.26C).

The oxide semiconductor films 111 and 111 a can be formed in such amanner that an oxide semiconductor film is formed over the insulatingfilm 116, the oxide semiconductor film is patterned so that a desiredregion thereof remains, and then unnecessary regions are etched.

Next, the insulating film 118 is formed over the insulating film 116 andthe oxide semiconductor films 111 and 111 a (see FIG. 27A).

The insulating film 118 includes one or both of hydrogen and nitrogen.As the insulating film 118, a silicon nitride film is preferably used,for example. The insulating film 118 can be formed by a sputteringmethod or a PECVD method, for example. In the case where the insulatingfilm 118 is formed by a PECVD method, for example, the substratetemperature is lower than 400° C., preferably lower than 375° C.,further preferably higher than or equal to 180° C. and lower than orequal to 350° C. The substrate temperature at which the insulating film118 is formed is preferably within the above range because a dense filmcan be formed. Furthermore, when the substrate temperature at which theinsulating film 118 is formed is within the above range, oxygen orexcess oxygen in the insulating films 114 and 116 can be moved to theoxide semiconductor film 110.

After the insulating film 118 is formed, heat treatment similar to thefirst heat treatment (hereinafter referred to as second heat treatment)may be performed. Through such heat treatment at lower than 400° C.,preferably lower than 375° C., further preferably higher than or equalto 180° C. and lower than or equal to 350° C. after the addition ofoxygen to the insulating film 116 when the oxide semiconductor film tobe the oxide semiconductor films 111 and 111 a is formed, oxygen orexcess oxygen in the insulating film 116 can be moved into the oxidesemiconductor film 110 and compensate oxygen vacancies in the oxidesemiconductor film 110.

Oxygen moved to the oxide semiconductor film 110 is described withreference to FIG. 28. FIG. 28 are model diagrams illustrating oxygenmoved to the oxide semiconductor film 110 due to the substratetemperature at the time of forming the insulating film 118 (typically,lower than 375° C.) or the second heat treatment after the formation ofthe insulating film 118 (typically, lower than 375° C.). In FIG. 28,oxygen (oxygen radicals, oxygen atoms, or oxygen molecules) moved to theoxide semiconductor film 110 is shown by arrows of broken lines. Notethat FIG. 28 is a cross-sectional view of the transistor 150 after theinsulating film 118 is formed and its periphery.

In the oxide semiconductor film 110 in FIG. 28, oxygen vacancies arecompensated with oxygen moved from films in contact with the oxidesemiconductor film 110 (here, the insulating film 107 and the insulatingfilm 114). Specifically, in the touch panel of one embodiment of thepresent invention, the insulating film 107 includes an excess oxygenregion because an oxygen gas is used at the time of forming the oxidesemiconductor film to be the oxide semiconductor film 110 by sputteringand oxygen is added to the insulating film 107. Furthermore, theinsulating film 116 includes an excess oxygen region because an oxygengas is used at the time of forming the oxide semiconductor film to bethe oxide semiconductor film 111 by sputtering and oxygen is added tothe insulating film 116. In the oxide semiconductor film 110 between theinsulating films including the excess oxygen regions, oxygen vacanciescan be favorably compensated.

Furthermore, the insulating film 106 is provided under the insulatingfilm 107, and the insulating film 118 is provided over the insulatingfilms 114 and 116. When the insulating films 106 and 118 are formedusing a material having low oxygen permeability, e.g., silicon nitride,oxygen contained in the insulating films 107, 114, and 116 can beconfined to the oxide semiconductor film 110 side; thus, oxygen can befavorably moved to the oxide semiconductor film 110. Note that theinsulating film 118 also has an advantageous effect of preventing anexternal impurity such as water, alkali metal, or alkaline earth metal,from diffusing into the oxide semiconductor film 110 included in thetransistor 150.

The insulating film 118 contains one or both of hydrogen and nitrogen.Thus, one or both of hydrogen and nitrogen is added to the oxidesemiconductor films 111 and 111 a in contact with the formed insulatingfilm 118, so that the oxide semiconductor films 111 and 111 a have highcarrier density and can function as an oxide conductive film.

Note that since the resistivity of the oxide semiconductor films 111 and111 a is decreased, the oxide semiconductor films 111 and 111 a in FIG.27A are indicated by a different hatching pattern from that in FIG. 26C.At this stage, the transistor 150 is completed.

The resistivity of the oxide semiconductor films 111 and 111 a is lowerthan at least the resistivity of the oxide semiconductor film 110 and ispreferably higher than or equal to 1×10⁻³ Ωcm and lower than 1×10⁴ Ωcm,further preferably higher than or equal to 1×10⁻³ Ωcm and lower than1×10⁻¹ Ωcm.

Then, an opening 142 is formed as follows: the insulating film 119 isformed over the insulating film 118, the insulating films 118 and 119are patterned so that a desired region thereof remains, and unnecessaryregions are etched (see FIG. 27B).

The insulating film 119 can be formed using any of the materialsdescribed above. Note that in this embodiment, an acrylic resin is usedfor the insulating film 119.

The opening 142 is formed to expose part of the drain electrode 112 b.The opening 142 can be formed by a dry etching method, for example.Alternatively, a wet etching method or a combination of dry etching andwet etching can be employed for formation of the opening 142. Note thatthe etching step of forming the opening 142 can reduce the thickness ofthe drain electrode 112 b in some cases.

Note that the opening may be formed in the insulating films 114, 116,118, and 119 at one time in the step of forming the opening 142 withoutperforming the step of forming the opening 141. In this case, the numberof steps of manufacturing the touch panel of one embodiment of thepresent invention is reduced, resulting in a reduction of themanufacturing cost.

Then, a conductive film is formed over the insulating film 119 to coverthe opening 142 and is patterned so that a desired region thereofremains, and unnecessary regions are etched; thus, the conductive film120 is formed (see FIG. 27C).

The conductive film 120 can be formed using any of the materialsdescribed above. Note that in this embodiment, indium tin oxide is usedfor the conductive film 120.

The capacitor 160 is formed concurrently with the conductive film 120.The capacitor 160 includes a dielectric layer between a pair ofelectrodes. One of the pair of electrodes corresponds to the oxidesemiconductor film 111, and the other electrode corresponds to theconductive film 120. In addition, the insulating films 118 and 119 serveas a dielectric layer of the capacitor 160.

Through the above steps, the transistor 150 and the pair of electrodesincluded in the capacitor 160 and the liquid crystal element 308 in thetouch panel 310 illustrated in FIG. 8 can be formed.

Note that although the structure with the insulating film 119 is shownin FIG. 27C, a structure without the insulating film 119 may be employed(see FIG. 29A). In the structure in FIG. 29A, the insulating film 118serves as a dielectric film of the capacitor 160. Moreover, in thetransistor 150, a structure in which the gate electrode 104 is notprovided and the oxide semiconductor film 111 a serves as a first gateelectrode may be employed (see FIG. 29B). FIG. 29B differs from FIG. 27Cin that the gate electrode 104 and the insulating film 106 are notprovided. The transistor 150 illustrated in FIG. 29B is a so-calledtop-gate transistor.

The structures, the methods, and the like described in this embodimentcan be combined as appropriate with any of the structures, the methods,and the like described in the other embodiments.

Structure Example 2

In this structure example, an organic EL element is used as the displayelement included in the touch panel.

Cross-Sectional Structure Example 1

Examples of the cross-sectional structure of a touch panel of oneembodiment of the present invention are described below with referenceto the drawings. Note that the description of the portions alreadydescribed is omitted and different portions are described.

A touch panel 320 illustrated in FIG. 13 includes a light-emittingelement 280 in the display portion 381. The light-emitting element 280includes the conductive film 120, an EL layer 281, and a conductive film282. The conductive film 120 serving as a reflective film iselectrically connected to the drain electrode 112 b of the transistor150 via an opening provided in the insulating films 114, 116, 118, and119. The conductive film 282 is also referred to as a lower electrode. Amaterial transmitting visible light is used for the conductive film 282.Moreover, the conductive film 282 may serve as a semi-reflective film.The conductive film 282 can also be referred to as an upper electrode.By applying a voltage between the conductive films 120 and 282, lightemitted by a light-emitting layer included in the EL layer 281 can beextracted through a coloring film (e.g., the coloring film 331R)provided in the substrate 372. The touch panel 320 illustrated in FIG.13 includes a so-called top emission display device. Note that thespecific structure of the light-emitting element 280 is described laterin Embodiment 4.

An insulating film 391 serving as a partition is provided over theinsulating film 119. The insulating film 391 is provided to overlap withend portions of the conductive films 120 of two adjacent pixels. The ELlayer 281 is provided over the conductive film 120 and the insulatingfilm 391. The conductive film 282 is provided over the EL layer 281 tooverlap with at least the conductive film 120. For example, in the touchpanel 320 illustrated in FIG. 13, the conductive film 282 includes anopening 385 in a position overlapping with a space between twoconductive films 120 of two pixels that are adjacent in one direction.Alternatively, the conductive film 282 may include one opening 385 foreach block that includes a plurality of pixels that are adjacent in onedirection (e.g., 30 or 60 pixels) in a position overlapping with a spacebetween two conductive films 120 of two pixels that are adjacent to eachother in the one direction.

The oxide semiconductor film 111 is provided over the insulating film116 in a position overlapping with the opening 385. The oxidesemiconductor film 111 can be formed at the same time using the samematerial as the oxide semiconductor film 111 a serving as the secondgate electrode of the transistor 150.

The touch sensor included in the touch panel 320 is formed using theconductive film 334 that is provided over the substrate 372 and theoxide semiconductor film 111 that is provided over the substrate 102.With the use of capacitance formed between the conductive film 334 andthe oxide semiconductor film 111, the approach or contact of an objectcan be sensed.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 14 is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 320 illustrated in FIG. 13.The dashed-dotted line Z5-Z6 in FIG. 14 corresponds to the displayportion 381 in FIG. 13.

The conductive film 334 that is one electrode of the touch sensorextends in the Y direction. The oxide semiconductor film 111 that is theother electrode of the touch sensor extends in the X direction andintersects with the conductive film 334. Note that the conductive film334 may extend in the X direction and the oxide semiconductor film 111may extend in the Y direction.

In the touch panel 320, the substrate 102 and the substrate 372 areattached to each other with the sealant 151. A region surrounded by thesubstrate 102, the substrate 372, and the sealant 151 is a hollow;however, the region may be filled with a sealant. An insulating film isnot provided over the coloring films 331R and 331G and thelight-blocking film 332; however, the above-described insulating film355 serving as an overcoat may be provided.

The EL layer 281 is shared by a plurality of pixels in thelight-emitting element 280 in FIG. 13; however, the EL layer 281 may beprovided for each pixel (see FIG. 15). In this case, the EL layer 281including a light-emitting layer emitting light whose color correspondsto emission color required by a pixel may be provided for each pixel. Astructure without a coloring film (e.g., the coloring films 331R and331G) may be employed.

[Cross-Sectional Structure Example 2]

FIG. 16 illustrates a cross-sectional structure example of a touch panelthat partly differs from the structure of FIG. 13. Note thatdescriptions of the portions already described are omitted and differentportions are described.

FIG. 16 has a structure in which the conductive films 334 and 341 andthe FPC 375 are not provided on the display surface side of thesubstrate 372. The oxide semiconductor film 111 formed at the same timeusing the same material as the second gate electrode of the transistor150 serves as the pair of electrodes of the touch sensor. Specifically,the oxide semiconductor film 111 b (not illustrated) that extends in onedirection and the oxide semiconductor film 111 c that is electricallyconnected to the conductive film 104 a extending in the directionorthogonal to the oxide semiconductor film 111 b serve as the pair ofelectrodes of the touch sensor. With such a structure, the processingsteps can be simpler than those of the structure illustrated in FIG. 13.Note that the oxide semiconductor film 111 c is electrically connectedto the conductive film 104 a via the opening 333 provided in theinsulating films 108, 114, and 116. The conductive film 104 a can beformed at the same time using the same material as the gate electrode104.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 17 is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 320 illustrated in FIG. 16.The dashed-dotted line Z7-Z8 in FIG. 17 corresponds to the displayportion 381 in FIG. 16.

The oxide semiconductor film 111 b that is one electrode of the touchsensor extends in the Y direction. The oxide semiconductor film 111 cthat is the other electrode of the touch sensor is electricallyconnected to the conductive film 104 a via the opening 333. Theconductive film 104 a extends in the X direction and intersects with theoxide semiconductor film 111 b.

The conductive film 282 serving as one electrode of the light-emittingelement 280 may serve as the other electrode of the touch sensor. In thetouch panel 320 in FIG. 18, the oxide semiconductor film 111 that is theone electrode of the touch sensor extends in the X direction. Theconductive film 282 extends in the Y direction and intersects with theoxide semiconductor film 111. FIG. 19 is a schematic top view of thepair of electrodes of the touch sensor included in the touch panel 320illustrated in FIG. 18. The dashed-dotted line Z9-Z10 in FIG. 19corresponds to the display portion 381 in FIG. 18. The opening 385included in the conductive film 282 extends in the direction orthogonalto the direction in which the oxide semiconductor film 111 extends. Partof the opening 385 overlaps with the oxide semiconductor film 111.

[Cross-Sectional Structure Example 3]

FIG. 20 illustrates a cross-sectional structure example of a touch panelthat partly differs from the above-described structure example. Notethat descriptions of the portions already described are omitted anddifferent portions are described.

A touch panel 320 illustrated in FIG. 20 includes the light-emittingelement 280 in the display portion 381. The light-emitting element 280includes a conductive film 285, the EL layer 281, and a conductive film286. The conductive film 285 is electrically connected to the drainelectrode 112 b of the transistor 150 via an opening provided in theinsulating films 114, 116, 118, and 119. A material transmitting visiblelight is used for the conductive film 285. Moreover, the conductive film285 may serve as a semi-reflective film. The conductive film 286 servesas a reflective film. By applying a voltage between the conductive films285 and 286, light emitted by a light-emitting layer included in the ELlayer 281 can be extracted through a coloring film (e.g., the coloringfilm 331R) provided in the substrate 102. The touch panel 320illustrated in FIG. 20 includes a display device having a so-calledbottom emission structure.

The light-blocking film 332 and the coloring films 331R and 331G areprovided over the insulating film 118. The light-blocking film 332 isprovided in a position overlapping with the insulating film 391. Thecoloring films 331R and 331G are provided in a position overlapping withthe conductive film 285. The EL layer 281 and the conductive film 286are provided in this order over the conductive film 285.

The conductive films 334 and 341 and the FPC 375 are provided on thedisplay surface side (the side opposite to the substrate 372) of thesubstrate 102. A touch sensor included in the touch panel 320 is formedusing the conductive film 334 and the oxide semiconductor film 111 thatserve as a pair of electrodes. With the conductive film 334 provided onthe display surface side of the substrate 102, another conductive film(e.g., the conductive film 285 and the conductive film 286) is notinterposed between the pair of electrodes. The oxide semiconductor film111 transmits visible light and thus can be provided in a regionoverlapping with the conductive film 285 through which light emittedfrom the light-emitting element 280 passes. Accordingly, the oxidesemiconductor film 111 can be provided in a large area; thus, thecapacitance of the touch sensor can be large.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 21 is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 320 illustrated in FIG. 20.The dashed-dotted line Z11-Z12 in FIG. 21 corresponds to the displayportion 381 in FIG. 20.

The conductive film 334 that is one electrode of the touch sensorextends in the Y direction. The oxide semiconductor film 111 that is theother electrode of the touch sensor extends in the X direction andintersects with the conductive film 334. Note that the conductive film334 may extend in the X direction and the oxide semiconductor film 111may extend in the Y direction.

Although the EL layer 281 is shared by a plurality of pixels in thelight-emitting element 280 in FIG. 20, the EL layer 281 may be providedfor each pixel (see FIG. 22). In this case, the EL layer 281 including alight-emitting layer emitting light whose color corresponds to colorrequired to a pixel may be provided for each pixel. A structure withouta coloring film (e.g., the coloring films 331R and 331G) may beemployed.

[Cross-Sectional Structure Example 4]

FIG. 23 illustrates a cross-sectional structure example of a touch panelthat partly differs from the structure of FIG. 20. Note thatdescriptions of the portions already described are omitted and differentportions are described.

FIG. 23 has a structure in which the conductive films 334 and 341 andthe FPC 375 are not provided on the display surface side of thesubstrate 102. The oxide semiconductor film 111 formed at the same timeusing the same material as the second gate electrode of the transistor150 serves as the pair of electrodes of the touch sensor. Specifically,the oxide semiconductor film 111 b that extends in one direction and theoxide semiconductor film 111 c that is electrically connected to theconductive film 104 a extending in the direction orthogonal to the oxidesemiconductor film 111 b serve as the pair of electrodes of the touchsensor. With such a structure, the processing steps can be simpler thanthose of the structure illustrated in FIG. 20. Note that the oxidesemiconductor film 111 c is electrically connected to the conductivefilm 104 a via the opening 333 provided in the insulating films 108,114, and 116. The conductive film 104 a can be formed at the same timeusing the same material as the gate electrode 104. It is preferable thatthe conductive film 104 a be provided in a region overlapping with thelight-blocking film 332 because the pair of electrodes of the touchsensor is formed with the aperture ratio of the pixel maintained.

Here, the arrangement of the electrodes included in the touch sensor isdescribed. FIG. 24 is a schematic top view of the pair of electrodes ofthe touch sensor included in the touch panel 320 illustrated in FIG. 23.The dashed-dotted line Z13-Z14 in FIG. 24 corresponds to the displayportion 381 in FIG. 23.

The oxide semiconductor film 111 b that is one electrode of the touchsensor extends in the Y direction. The oxide semiconductor film 111 cthat is the other electrode of the touch sensor is electricallyconnected to the conductive film 104 a via the opening 333. Theconductive film 104 a extends in the X direction and intersects with theoxide semiconductor film 111 b.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

In this embodiment, an example of an oxide semiconductor that can beused for the transistor and the capacitor of the liquid crystal displaydevice of one embodiment of the present invention is described. Thestructure of an oxide semiconductor is described below.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.In addition, the term “substantially parallel” indicates that the angleformed between two straight lines is greater than or equal to −30° andless than or equal to 30°. The term “perpendicular” indicates that theangle formed between two straight lines is greater than or equal to 80°and less than or equal to 100°, and accordingly also includes the casewhere the angle is greater than or equal to 85° and less than or equalto 95°. In addition, the term “substantially perpendicular” indicatesthat the angle formed between two straight lines is greater than orequal to 60° and less than or equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

Oxide semiconductors are classified into a single crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofa non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a nanocrystalline oxide semiconductor (nc-OS), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

From another perspective, oxide semiconductors are classified into anamorphous oxide semiconductor and a crystalline oxide semiconductor.Examples of a crystalline oxide semiconductor include a single crystaloxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor,and an nc-OS.

It is known that an amorphous structure is generally defined as beingmetastable and unfixed, and being isotropic and having no non-uniformstructure. In other words, an amorphous structure has a flexible bondangle and a short-range order but does not have a long-range order.

This means that an inherently stable oxide semiconductor cannot beregarded as a completely amorphous oxide semiconductor. Moreover, anoxide semiconductor that is not isotropic (e.g., an oxide semiconductorthat has a periodic structure in a microscopic region) cannot beregarded as a completely amorphous oxide semiconductor. Note that ana-like OS has a periodic structure in a microscopic region, but at thesame time contains a void and has an unstable structure. For thisreason, an a-like OS has physical properties similar to those of anamorphous oxide semiconductor.

<CAAC-OS>

First, a CAAC-OS is described.

A CAAC-OS is an oxide semiconductor having a plurality of c-axis alignedcrystal parts (also referred to as pellets).

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OS,which is obtained using a transmission electron microscope (TEM), aplurality of pellets can be observed. However, in the high-resolutionTEM image, a boundary between pellets, that is, a grain boundary is notclearly observed. Thus, in the CAAC-OS, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

The CAAC-OS observed with a TEM is described below. FIG. 30A shows ahigh-resolution TEM image of a cross section of the CAAC-OS observedfrom the direction substantially parallel to the sample surface. Thehigh-resolution TEM image is obtained with a spherical aberrationcorrector function. The high-resolution TEM image obtained with aspherical aberration corrector function is particularly referred to as aCs-corrected high-resolution TEM image. The Cs-corrected high-resolutionTEM image can be obtained with, for example, an atomic resolutionanalytical electron microscope JEM-ARM200F manufactured by JEOL Ltd.

FIG. 30B is an enlarged Cs-corrected high-resolution TEM image of aregion (1) in FIG. 30A. FIG. 30B shows that metal atoms are arranged ina layered manner in a pellet. Each metal atom layer has a configurationreflecting unevenness of a surface over which the CAAC-OS is formed(hereinafter, the surface is referred to as a formation surface) or atop surface of the CAAC-OS, and is arranged parallel to the formationsurface or the top surface of the CAAC-OS.

As shown in FIG. 30B, the CAAC-OS has a characteristic atomicarrangement. The characteristic atomic arrangement is denoted by anauxiliary line in FIG. 30C. FIGS. 30B and 30C prove that the size of apellet is greater than or equal to 1 nm or greater than or equal to 3nm, and the size of a space caused by the tilt of the pellets isapproximately 0.8 nm. Therefore, the pellet can also be referred to as ananocrystal (nc). Note that a CAAC-OS can be referred to as an oxidesemiconductor including c-axis aligned nanocrystals (CANC).

Here, according to the Cs-corrected high-resolution TEM images, theschematic arrangement of pellets 5100 of a CAAC-OS over a substrate 5120is illustrated by such a structure in which bricks or blocks are stacked(see FIG. 30D). The part in which the pellets are tilted as observed inFIG. 30C corresponds to a region 5161 illustrated in FIG. 30D.

FIG. 31A shows a Cs-corrected high-resolution TEM image of a plane ofthe CAAC-OS film observed from the direction substantially perpendicularto the sample surface. FIGS. 31B, 31C, and 31D are enlarged Cs-correctedhigh-resolution TEM images of regions (1), (2), and (3) in FIG. 31A,respectively. FIGS. 31B, 31C, and 31D indicate that metal atoms arearranged in a triangular, quadrangular, or hexagonal configuration in apellet. However, there is no regularity of arrangement of metal atomsbetween different pellets.

Next, a CAAC-OS analyzed by X-ray diffraction (XRD) is described. Forexample, when the structure of a CAAC-OS including an InGaZnO₄ crystalis analyzed by an out-of-plane method, a peak appears at a diffractionangle (2θ) of around 31° as shown in FIG. 32A. This peak is derived fromthe (009) plane of the InGaZnO₄ crystal, which indicates that crystalsin the CAAC-OS have c-axis alignment, and that the c-axes are aligned inthe direction substantially perpendicular to the formation surface orthe top surface of the CAAC-OS.

Note that in structural analysis of the CAAC-OS by an out-of-planemethod, another peak may appear when 2θ is around 36°, in addition tothe peak at 2θ of around 31°. The peak at 2θ of around 36° indicatesthat a crystal having no c-axis alignment is included in part of theCAAC-OS. In a preferable CAAC-OS whose structure is analyzed by anout-of-plane method, a peak appears when 2θ is around 31° and no peakappears when 2θ is around 36°.

On the other hand, in structural analysis of the CAAC-OS by an in-planemethod in which an X-ray is incident on a sample in the directionsubstantially perpendicular to the c-axis, a peak appears when 2θ isaround 56°. This peak is attributed to the (110) plane of the InGaZnO₄crystal. In the case of the CAAC-OS, when analysis (ϕ scan) is performedwith 2θ fixed at around 56° and with the sample rotated using a normalvector of the sample surface as an axis (ϕ axis), as shown in FIG. 32B,a peak is not clearly observed. In contrast, in the case of a singlecrystal oxide semiconductor of InGaZnO₄, when ϕ scan is performed with2θ fixed at around 56°, as shown in FIG. 32C, six peaks that are derivedfrom crystal planes equivalent to the (110) plane are observed.Accordingly, the structural analysis using XRD shows that the directionsof a-axes and b-axes are irregularly oriented in the CAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction is described. Forexample, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in the directionparallel to the sample surface, such a diffraction pattern (alsoreferred to as a selected-area transmission electron diffractionpattern) as is shown in FIG. 33A can be obtained. In this diffractionpattern, spots derived from the (009) plane of an InGaZnO₄ crystal areincluded. Thus, the electron diffraction also indicates that pelletsincluded in the CAAC-OS have c-axis alignment and that the c-axes arealigned in the direction substantially perpendicular to the formationsurface or the top surface of the CAAC-OS. Meanwhile, FIG. 33B shows adiffraction pattern obtained in such a manner that an electron beam witha probe diameter of 300 nm is incident on the same sample in thedirection perpendicular to the sample surface. As shown in FIG. 33B, aring-like diffraction pattern is observed. Thus, the electrondiffraction also indicates that the a-axes and b-axes of the pelletsincluded in the CAAC-OS do not have regular alignment. The first ring inFIG. 33B is probably derived from the (010) plane, the (100) plane, andthe like of the InGaZnO₄ crystal. The second ring in FIG. 33B isprobably derived from the (110) plane and the like.

As described above, the CAAC-OS is an oxide semiconductor with highcrystallinity. Entry of impurities, formation of defects, or the likemight decrease the crystallinity of an oxide semiconductor. This meansthat the CAAC-OS has small amounts of impurities and defects (e.g.,oxygen vacancies).

Note that the impurity means an element other than the main componentsof the oxide semiconductor, such as hydrogen, carbon, silicon, or atransition metal element. For example, an element (specifically, siliconor the like) having higher strength of bonding to oxygen than a metalelement included in an oxide semiconductor extracts oxygen from theoxide semiconductor, which results in disorder of the atomic arrangementand reduced crystallinity of the oxide semiconductor. A heavy metal suchas iron or nickel, argon, carbon dioxide, or the like has a large atomicradius (or molecular radius), and thus disturbs the atomic arrangementof the oxide semiconductor and decreases crystallinity.

The characteristics of an oxide semiconductor having impurities ordefects might be changed by light, heat, or the like. For example, theimpurity contained in the oxide semiconductor might serve as a carriertrap or serve as a carrier generation source. Furthermore, oxygenvacancies in the oxide semiconductor might serve as carrier traps orserve as carrier generation sources when hydrogen is captured therein.

The CAAC-OS having small amounts of impurities and oxygen vacancies isan oxide semiconductor with low carrier density (specifically, lowerthan 8×10¹¹/cm³, preferably lower than 1×10¹¹/cm³, more preferably lowerthan 1×10¹⁰/cm³, and is higher than or equal to 1×10⁻⁹/cm³). Such anoxide semiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.Thus, the CAAC-OS can be referred to as an oxide semiconductor havingstable characteristics.

<nc-OS>

Next, an nc-OS is described.

An nc-OS has a region in which a crystal part is observed and a regionin which a crystal part is not clearly observed in a high-resolution TEMimage. In most cases, the size of a crystal part included in the nc-OSis greater than or equal to 1 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 3 nm. An oxidesemiconductor including a crystal part whose size is greater than 10 nmand less than or equal to 100 nm can be referred to as amicrocrystalline oxide semiconductor. In a high-resolution TEM image ofthe nc-OS, for example, a grain boundary is not clearly observed in somecases. Note that there is a possibility that the origin of thenanocrystal is the same as that of a pellet in a CAAC-OS. Therefore, acrystal part of the nc-OS may be referred to as a pellet in thefollowing description.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different pellets in thenc-OS. Thus, the orientation of the whole film is not ordered.Accordingly, the nc-OS cannot be distinguished from an a-like OS or anamorphous oxide semiconductor, depending on an analysis method. Forexample, when the nc-OS is subjected to analysis by an out-of-planemethod using an X-ray having a diameter larger than the size of apellet, a peak that shows a crystal plane does not appear. Furthermore,a diffraction pattern like a halo pattern is observed when the nc-OS issubjected to electron diffraction using an electron beam with a probediameter (e.g., 50 nm or larger) that is larger than the size of apellet. Meanwhile, spots appear in a nanobeam electron diffractionpattern of the nc-OS when an electron beam having a probe diameter closeto or smaller than the size of a pellet is applied. Moreover, in ananobeam electron diffraction pattern of the nc-OS, regions with highluminance in a circular (ring) pattern are shown in some cases.Furthermore, a plurality of spots is shown in a ring-like region in somecases.

Since there is no regularity of crystal orientation between the pellets(nanocrystals) as mentioned above, the nc-OS can also be referred to asan oxide semiconductor including random aligned nanocrystals (RANC) oran oxide semiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has high regularity as comparedwith an amorphous oxide semiconductor. Therefore, the nc-OS has a lowerdensity of defect states than an a-like OS and an amorphous oxidesemiconductor. Note that there is no regularity of crystal orientationbetween different pellets in the nc-OS. Therefore, the nc-OS has ahigher density of defect states than the CAAC-OS.

<A-like OS>

An a-like OS has a structure between those of the nc-OS and theamorphous oxide semiconductor.

In a high-resolution TEM image of the a-like OS, a void may be observed.Furthermore, in the high-resolution TEM image, there are a region wherea crystal part is clearly observed and a region where a crystal part isnot observed.

The a-like OS has an unstable structure because it contains a void. Toverify that an a-like OS has an unstable structure as compared with aCAAC-OS and an nc-OS, a change in structure caused by electronirradiation is described below.

An a-like OS (referred to as Sample A), an nc-OS (referred to as SampleB), and a CAAC-OS (referred to as Sample C) are prepared as samplessubjected to electron irradiation. Each of the samples is an In—Ga—Znoxide.

First, a high-resolution cross-sectional TEM image of each sample isobtained. The high-resolution cross-sectional TEM images show that allthe samples have crystal parts.

Note that which part is regarded as a crystal part is determined asfollows. It is known that a unit cell of an InGaZnO₄ crystal has astructure in which nine layers including three In—O layers and sixGa—Zn—O layers are stacked in the c-axis direction. The distance betweenthe adjacent layers is equivalent to the lattice spacing on the (009)plane (also referred to as d value). The value is calculated to be 0.29nm from crystal structural analysis. Accordingly, a portion where thelattice spacing between lattice fringes is greater than or equal to 0.28nm and less than or equal to 0.30 nm is regarded as a crystal part ofInGaZnO₄. Each of lattice fringes corresponds to the a-b plane of theInGaZnO₄ crystal.

FIG. 34 shows change in the average size of crystal parts (at 22 pointsto 45 points) in each sample. Note that the crystal part sizecorresponds to the length of a lattice fringe. FIG. 34 indicates thatthe crystal part size in the a-like OS increases with an increase in thecumulative electron dose. Specifically, as shown by (1) in FIG. 34, acrystal part of approximately 1.2 nm (also referred to as an initialnucleus) at the start of TEM observation grows to a size ofapproximately 2.6 nm at a cumulative electron dose of 4.2×10⁸ e⁻/nm². Incontrast, the crystal part size in the nc-OS and the CAAC-OS showslittle change from the start of electron irradiation to a cumulativeelectron dose of 4.2×10⁸ e⁻/nm². Specifically, as shown by (2) and (3)in FIG. 34, the average size of crystal parts in an nc-OS and a CAAC-OSare approximately 1.4 nm and approximately 2.1 nm, respectively,regardless of the cumulative electron dose.

In this manner, growth of the crystal part in the a-like OS is inducedby electron irradiation. In contrast, in the nc-OS and the CAAC-OS,growth of the crystal part is hardly induced by electron irradiation.Therefore, the a-like OS has an unstable structure as compared with thenc-OS and the CAAC-OS.

The a-like OS has a lower density than the nc-OS and the CAAC-OS becauseit contains a void. Specifically, the density of the a-like OS is higherthan or equal to 78.6% and lower than 92.3% of the density of the singlecrystal oxide semiconductor having the same composition. The density ofeach of the nc-OS and the CAAC-OS is higher than or equal to 92.3% andlower than 100% of the density of the single crystal oxide semiconductorhaving the same composition. Note that it is difficult to deposit anoxide semiconductor having a density of lower than 78% of the density ofthe single crystal oxide semiconductor.

For example, in the case of an oxide semiconductor having an atomicratio of In:Ga:Zn=1:1:1, the density of single crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, thedensity of the a-like OS is higher than or equal to 5.0 g/cm³ and lowerthan 5.9 g/cm³. For example, in the case of the oxide semiconductorhaving an atomic ratio of In:Ga:Zn=1:1:1, the density of each of thenc-OS and the CAAC-OS is higher than or equal to 5.9 g/cm³ and lowerthan 6.3 g/cm³.

Note that single crystals with the same composition do not exist in somecases. In that case, single crystal oxide semiconductors with differentcompositions are combined at an adequate ratio, which makes it possibleto estimate density equivalent to that of a single crystal oxidesemiconductor with the desired composition. The density of a singlecrystal oxide semiconductor having the desired composition can beestimated using a weighted average according to the combination ratio ofthe single crystal oxide semiconductors with different compositions.Note that it is preferable to use as few kinds of single crystal oxidesemiconductors as possible to estimate the density.

As described above, oxide semiconductors have various structures andvarious properties. Note that an oxide semiconductor may be a stackincluding two or more of an amorphous oxide semiconductor, an a-like OS,an nc-OS, and a CAAC-OS, for example.

<Method for Forming CAAC-OS>

An example of a method for forming a CAAC-OS film is described below.FIG. 35 is a schematic view of the inside of a deposition chamber. TheCAAC-OS film can be formed by a sputtering method.

As shown in FIG. 35, a substrate 5220 and a target 5230 are arranged toface each other. Plasma 5240 is generated between the substrate 5220 andthe target 5230. A heating mechanism 5260 is provided under thesubstrate 5220. Although not illustrated, a target 5230 is attached to abacking plate. A plurality of magnets is provided to face the target5230 with the backing plate positioned therebetween. A sputtering methodin which the deposition rate is increased by utilizing a magnetic fieldof magnets is referred to as a magnetron sputtering method.

The distance d between the substrate 5220 and the target 5230 (alsoreferred to as a target-substrate distance (T-S distance)) is greaterthan or equal to 0.01 m and less than or equal to 1 m, preferablygreater than or equal to 0.02 m and less than or equal to 0.5 m. Thedeposition chamber is mostly filled with a deposition gas (e.g., anoxygen gas, an argon gas, or a mixed gas containing oxygen at 5 vol % orhigher) and the pressure in the deposition chamber is controlled to behigher than or equal to 0.01 Pa and lower than or equal to 100 Pa,preferably higher than or equal to 0.1 Pa and lower than or equal to 10Pa. Here, discharge starts by application of a certain voltage or higherto the target 5230, and plasma 5240 is observed. The magnetic fieldforms a high-density plasma region in the vicinity of the target 5230.In the high-density plasma region, the deposition gas is ionized, sothat an ion 5201 is generated. Examples of the ion 5201 include anoxygen cation (O⁺) and an argon cation (Ar⁺).

Here, the target 5230 has a polycrystalline structure with a pluralityof crystal grains and in which a cleavage plane exists in any of thecrystal grains. FIGS. 36A to 36C show a crystal structure of InMZnO₄(the element M is Al, Ga, Y, or Sn, for example) included in the target5230 as an example. Note that FIG. 36A illustrates the crystal structureof InMZnO₄ observed from the direction parallel to the b-axis. In thecrystal of InMZnO₄, oxygen atoms are negatively charged, wherebyrepulsive force is generated between the two adjacent M-Zn—O layers.Thus, the InMZnO₄ crystal has a cleavage plane between the two adjacentM-Zn—O layers.

The ion 5201 generated in the high-density plasma region is acceleratedtoward the target 5230 side by an electric field, and then collides withthe target 5230. At this time, a pellet 5200 that is a flat-plate-likeor pellet-like sputtered particle is separated from the cleavage plane(FIG. 35). The pellet 5200 is between the two cleavage planes shown inFIG. 36A. Thus, when the pellet 5200 is observed, the cross-sectionthereof is as shown in FIG. 36B, and the top surface thereof is as shownin FIG. 36C. Note that the structure of the pellet 5200 may be distortedby an impact of collision of the ion 5201.

The pellet 5200 is a flat-plate-like (pellet-like) sputtered particlehaving a triangle plane, e.g., a regular triangle plane. Alternatively,the pellet 5200 is a flat-plate-like (pellet-like) sputtered particlehaving a hexagonal plane, e.g., regular hexagonal plane. The shape ofthe pellet 5200 is not limited to a triangle or a hexagon. For example,the flat plane may have a shape formed by combining two or moretriangles. For example, a quadrangle (e.g., rhombus) may be formed bycombining two triangles (e.g., regular triangles).

The thickness of the pellet 5200 is determined depending on the kind ofdeposition gas and the like. For example, the thickness of the pellet5200 is greater than or equal to 0.4 nm and less than or equal to 1 nm,preferably greater than or equal to 0.6 nm and less than or equal to 0.8nm. In addition, for example, the width of the pellet 5200 is greaterthan or equal to 1 nm and less than or equal to 100 nm, preferablygreater than or equal to 2 nm and less than or equal to 50 nm, morepreferably greater than or equal to 3 nm and less than or equal to 30nm. For example, the ion 5201 collides with the target 5230 includingthe In-M-Zn oxide. Then, the pellet 5200 including three layers of anM-Zn—O layer, an In—O layer, and an M-Zn—O layer is separated. Note thatalong with the separation of the pellet 5200, a particle 5203 is alsosputtered from the target 5230. The particle 5203 has an atom or anaggregate of several atoms. Therefore, the particle 5203 can be referredto as an atomic particle.

The surface of the pellet 5200 may be negatively or positively chargedwhen the pellet 5200 passes through the plasma 5240. For example, thepellet 5200 may receive a negative charge from O²⁻ in the plasma 5240.As a result, oxygen atoms on the surfaces of the pellet 5200 may benegatively charged. In addition, when passing through the plasma 5240,the pellet 5200 is sometimes combined with indium, the element M, zinc,oxygen, or the like in the plasma 5240 to grow up.

The pellet 5200 and the particles 5203 that have passed through theplasma 5240 reach a surface of the substrate 5220. Note that some of theparticles 5203 are discharged to the outside by a vacuum pump or thelike because of their smallness in mass.

Next, deposition of the pellet 5200 and the particle 5203 on the surfaceof the substrate 5220 is described with reference to FIGS. 37A to 37F.

First, a first pellet 5200 is deposited on the substrate 5220. Since thepellet 5200 has a flat-plate-like shape, it is deposited so that itsflat plane faces the surface of the substrate 5220. At this time, chargeon a surface of the pellet 5200 on the substrate 5220 side is lostthrough the substrate 5220.

Next, a second pellet 5200 reaches the substrate 5220. Since a surfaceof the first pellet 5200 and a surface of the second pellet 5200 arecharged, they repel each other. As a result, the second pellet 5200avoids being deposited on the first pellet 5200, and is deposited withits flat plane facing the surface of the substrate 5220 so as to be alittle distance away from the first pellet 5200. With repetition ofthis, millions of the pellets 5200 are deposited on the surface of thesubstrate 5220 to have a thickness of one layer. A region where nopellet 5200 is deposited is generated between adjacent pellets 5200 (seeFIG. 37A).

Then, the particles 5203 that have received energy from plasma reach thesurface of the substrate 5220. The particles 5203 cannot be deposited onan active region such as the surfaces of the pellets 5200. For thisreason, the particles 5203 move to regions where no pellet 5200 isdeposited and are attached to side surfaces of the pellets 5200. Sinceavailable bonds of the particles 5203 are activated by energy receivedfrom plasma, the particles 5203 are chemically bonded to the pellets5200 to form lateral growth portions 5202 (see FIG. 37B).

The lateral growth portions 5202 then further grow laterally so that thepellets 5200 are anchored to each other (see FIG. 37C). In this manner,the lateral growth portions 5202 are formed until they fill regionswhere no pellet 5200 is deposited. This mechanism is similar to adeposition mechanism for an atomic layer deposition (ALD) method.

Even when the deposited pellets 5200 are oriented in differentdirections, the particles 5203 cause a lateral growth to fill gapsbetween the pellets 5200; thus, no clear grain boundary is formed. Inaddition, as the particles 5203 make a smooth connection between thepellets 5200, a crystal structure different from single crystal andpolycrystal structures is formed. In other words, a crystal structureincluding distortion between minute crystal regions (pellets 5200) isformed. Regions filling the gaps between the crystal regions aredistorted crystal regions, and thus, it is probably not appropriate tosay that the regions have an amorphous structure.

Next, new pellets 5200 are deposited with their flat planes facing thesurface of the substrate 5220 (see FIG. 37D). After that, the particles5203 are deposited so as to fill regions where no pellet 5200 isdeposited, thereby forming the lateral growth portions 5202 (see FIG.37E). In such a manner, the particles 5203 are attached to side surfacesof the pellets 5200 and the lateral growth portions 5202 cause a lateralgrowth so that the pellets 5200 in the second layer are anchored to eachother (see FIG. 37F). Deposition continues until the m-th layer (m is aninteger of two or more) is formed; as a result, a layered thin filmstructure is formed.

A deposition way of the pellets 5200 changes according to the surfacetemperature of the substrate 5220 or the like. For example, if thesurface temperature of the substrate 5220 is high, migration of thepellets 5200 occurs over the surface of the substrate 5220. As a result,the proportion of the pellets 5200 that are directly connected with eachother without the particles 5203 increases, whereby a CAAC-OS film withhigh orientation is made. The surface temperature of the substrate 5220for formation of the CAAC-OS film is higher than or equal to roomtemperature and lower than 340° C., preferably higher than or equal toroom temperature and lower than or equal to 300° C., more preferablyhigher than or equal to 100° C. and lower than or equal to 250° C.,still more preferably higher than or equal to 100° C. and lower than orequal to 200° C. Therefore, even when a large-sized substrate of the 8thgeneration or more is used as the substrate 5220, a warp or the like dueto the formation of the CAAC-OS film hardly occurs.

In contrast, if the surface temperature of the substrate 5220 is low,the migration of the pellets 5200 over the substrate 5220 does noteasily occur. As a result, the pellets 5200 are stacked to form an nc-OSor the like with low orientation. In the nc-OS, the pellets 5200 arepossibly deposited with certain gaps when the pellets 5200 arenegatively charged. Therefore, the nc-OS has low orientation but someregularity, and thus it has a denser structure than an amorphous oxidesemiconductor.

When spaces between pellets are extremely small in a CAAC-OS, thepellets may apparently form a large pellet. The large pellet has asingle crystal structure. For example, the size of the large pellet maybe greater than or equal to 10 nm and less than or equal to 200 nm,greater than or equal to 15 nm and less than or equal to 100 nm, orgreater than or equal to 20 nm and less than or equal to 50 nm, whenseen from the above.

The pellets are probably deposited on the surface of the substrateaccording to such a deposition model. A CAAC-OS film can be formed evenwhen a formation surface does not have a crystal structure. Thisindicates that the above-described deposition model, which is a growthmechanism different from an epitaxial growth, has high validity. Inaddition, with the above-described deposition model, a uniform film of aCAAC-OS or an nc-OS can be formed even over a large-sized glasssubstrate or the like. Even when the surface of the substrate (formationsurface) has an amorphous structure (e.g., amorphous silicon oxide), forexample, a CAAC-OS film can be formed.

In addition, even when the surface of the substrate (formation surface)has an uneven shape, the pellets are aligned along the shape.

The above-described deposition model suggests that a CAAC-OS film withhigh crystallinity can be formed in the following manner: deposition isperformed in a high vacuum to have a long mean free path, plasma energyis weakened to reduce damage around a substrate, and thermal energy isapplied to a formation surface to repair damage due to plasma duringdeposition.

The above-described deposition model can be used not only for the casewhere a target has a polycrystalline structure of a composite oxide witha plurality of crystal grains, such as an In-M-Zn oxide, and any of thecrystal grains have a cleavage plane; but also for the case where, forexample, a target of a mixture containing indium oxide, an oxide of theelement M, and zinc oxide is used.

Since there is no cleavage plane in a target of a mixture, atomicparticles are separated from the target by sputtering. Duringdeposition, a high electric field region of plasma is formed around atarget. Because of the high electric field region of plasma, atomicparticles separated from the target are anchored to each other to causea lateral growth. For example, indium atoms, which are atomic particles,are anchored to each other and cause a lateral growth to be ananocrystal formed of an In—O layer, and then an M-Zn—O layer is bondedabove and below the nanocrystalline In—O layer so as to complement thenanocrystalline In—O layer. In this manner, a pellet can be formed evenwhen a target of a mixture is used. Accordingly, the above-describeddeposition model can also be applied to the case of using a target of amixture.

Note that in the case where a high electric field region of plasma isnot formed around a target, only atomic particles separated from thetarget are deposited on a substrate surface. In that case, a lateralgrowth of an atomic particle might occur on the substrate surface.However, since the orientations of atomic particles are not the same,the crystal orientation in the resulting thin film is not uniform. As aresult, an nc-OS or the like is obtained.

Embodiment 3

In this embodiment, a structure example different from that of thetransistor described in Embodiment 1 is described with reference toFIGS. 38A to 38C, FIGS. 39A to 39D, FIGS. 40A and 40B, and FIGS. 41A to41D.

Example 1 of Transistor Structure

FIG. 38A is a top view of a transistor 270. FIG. 38B is across-sectional view taken along the dashed-dotted line A1-A2 in FIG.38A, and FIG. 38C is a cross-sectional view taken along thedashed-dotted line B1-B2 in FIG. 38A. Note that the direction of thedashed dotted line A1-A2 may be called the channel length direction, andthe direction of the dashed dotted line B1-B2 may be called the channelwidth direction.

The transistor 270 includes a conductive film 204 functioning as a firstgate electrode over a substrate 202, an insulating film 206 over thesubstrate 202 and the conductive film 204, an insulating film 207 overthe insulating film 206, an oxide semiconductor film 208 over theinsulating film 207, a conductive film 212 a functioning as a sourceelectrode electrically connected to the oxide semiconductor film 208, aconductive film 212 b functioning as a drain electrode electricallyconnected to the oxide semiconductor film 208, insulating films 214 and216 over the oxide semiconductor film 208 and the conductive films 212 aand 212 b, and an oxide semiconductor film 211 b over the insulatingfilm 216. In addition, an insulating film 218 is provided over the oxidesemiconductor film 211 b.

In the transistor 270, the insulating films 214 and 216 function as asecond gate insulating film of the transistor 270. An oxidesemiconductor film 211 a is connected to the conductive film 212 bthrough an opening 252 c provided in the insulating films 214 and 216.The oxide semiconductor film 211 a functions as, for example, a pixelelectrode used for a display device. The oxide semiconductor film 211 bin the transistor 270 functions as a second gate electrode (alsoreferred to as a back gate electrode).

As illustrated in FIG. 38C, the oxide semiconductor film 211 b isconnected to the conductive film 204 functioning as a first gateelectrode through openings 252 a and 252 b provided in the insulatingfilms 206, 207, 214, and 216. Accordingly, the oxide semiconductor film211 b and a conductive film 220 b are supplied with the same potential.

Note that although the structure in which the openings 252 a and 252 bare provided so that the oxide semiconductor film 211 b and theconductive film 204 are connected to each other is described in thisembodiment, one embodiment of the present invention is not limitedthereto. For example, a structure in which only one of the openings 252a and 252 b is provided so that the oxide semiconductor film 211 b andthe conductive film 204 are connected to each other, or a structure inwhich the openings 252 a and 252 b are not provided and the oxidesemiconductor film 211 b and the conductive film 204 are not connectedto each other may be employed. Note that in the case where the oxidesemiconductor film 211 b and the conductive film 204 are not connectedto each other, it is possible to apply different potentials to the oxidesemiconductor film 211 b and the conductive film 204.

As illustrated in FIG. 38B, the oxide semiconductor film 208 ispositioned to face each of the conductive film 204 functioning as afirst gate electrode and the oxide semiconductor film 211 b functioningas a second gate electrode, and is sandwiched between the two conductivefilms functioning as gate electrodes. The length in the channel lengthdirection and the length in the channel width direction of the oxidesemiconductor film 211 b functioning as a second gate electrode arelonger than that in the channel length direction and that in the channelwidth direction of the oxide semiconductor film 208, respectively. Thewhole oxide semiconductor film 208 is covered with the oxidesemiconductor film 211 b with the insulating films 214 and 216positioned therebetween. Since the oxide semiconductor film 211 bfunctioning as a second gate electrode is connected to the conductivefilm 204 functioning as a first gate electrode through the openings 252a and 252 b provided in the insulating films 206 and 207 and theinsulating films 214 and 216, a side surface of the oxide semiconductorfilm 208 in the channel width direction faces the oxide semiconductorfilm 211 b functioning as a second gate electrode with the insulatingfilms 214 and 216 positioned therebetween.

In other words, in the channel width direction of the transistor 270,the conductive film 204 functioning as a first gate electrode and theoxide semiconductor film 211 b functioning as a second gate electrodeare connected to each other through the openings provided in theinsulating films 206 and 207 functioning as first gate insulating filmsand the insulating films 214 and 216 functioning as second gateinsulating films; and the conductive film 204 and the oxidesemiconductor film 211 b surround the oxide semiconductor film 208 withthe insulating films 206 and 207 functioning as the first gateinsulating films and the insulating films 214 and 216 functioning as thesecond gate insulating films positioned therebetween.

Such a structure enables the oxide semiconductor film 208 included inthe transistor 270 to be electrically surrounded by electric fields ofthe conductive film 204 functioning as a first gate electrode and theoxide semiconductor film 211 b functioning as a second gate electrode. Adevice structure of a transistor, like that of the transistor 270, inwhich electric fields of a first gate electrode and a second gateelectrode electrically surround an oxide semiconductor film where achannel region is formed, can be referred to as a surrounded channel(s-channel) structure.

Since the transistor 270 has the s-channel structure, an electric fieldfor inducing a channel can be effectively applied to the oxidesemiconductor film 208 by the conductive film 204 functioning as a firstgate electrode; therefore, the current drive capability of thetransistor 270 can be improved and high on-state current characteristicscan be obtained. Since the on-state current can be increased, it ispossible to reduce the size of the transistor 270. In addition, sincethe transistor 270 is surrounded by the conductive film 204 functioningas a first gate electrode and the oxide semiconductor film 211 bfunctioning as a second gate electrode, the mechanical strength of thetransistor 270 can be increased.

Example 2 of Transistor Structure

Structure examples different from that of the transistor 270 in FIGS.38A to 38C are described with reference to FIGS. 39A to 39D. FIGS. 39Aand 39B illustrate a cross-sectional view illustrating a modificationexample of the transistor 270 in FIGS. 38B and 38C. FIGS. 39C and 39Dillustrate a cross-sectional view illustrating another modificationexample of the transistor 270 in FIGS. 38B and 38C.

A transistor 270A in FIGS. 39A and 39B is different from the transistor270 in FIGS. 38B and 38C in that the oxide semiconductor film 208 has athree-layer structure. Specifically, the oxide semiconductor film 208 ofthe transistor 270A includes an oxide semiconductor film 208 a, an oxidesemiconductor film 208 b, and an oxide semiconductor film 208 c.

A transistor 270B in FIGS. 39C and 39D is different from the transistor270 in FIGS. 38B and 38C in that the oxide semiconductor film 208 has atwo-layer structure. Specifically, the oxide semiconductor film 208 ofthe transistor 270B includes the oxide semiconductor film 208 b and theoxide semiconductor film 208 c.

The structure of the transistor 150 described in Embodiment 1 can bereferred to for the structures of the transistors 270, 270A, and 270B inthis embodiment. Thus, the material and the manufacturing method of thesubstrate 102 can be referred to for those of the substrate 202. Thematerial and the manufacturing method of the gate electrode 104 can bereferred to for those of the conductive film 204. The materials and themanufacturing methods of the insulating films 106 and 107 can bereferred to for those of the insulating films 206 and 207, respectively.The material and the manufacturing method of the oxide semiconductorfilm 110 can be referred to for those of the oxide semiconductor film208. The material and the manufacturing method of the oxidesemiconductor film 111 can be referred to for those of the oxidesemiconductor film 211 a and those of the oxide semiconductor film 211b. The material and the manufacturing method of the source electrode 112a and the drain electrode 112 b can be referred to for those of theconductive film 212 a and the conductive film 212 b. The materials andthe manufacturing methods of the insulating films 114, 116, and 118 canbe referred to for those of the insulating films 214, 216, and 218,respectively.

Here, a band structure including the oxide semiconductor film 208 andinsulating films in contact with the oxide semiconductor film 208 isdescribed with reference to FIGS. 40A and 40B.

FIG. 40A shows an example of a band structure in the thickness directionof a layered structure including the insulating film 207, the oxidesemiconductor films 208 a, 208 b, and 208 c, and the insulating film214. FIG. 40B shows an example of a band structure in the thicknessdirection of a layered structure including the insulating film 207, theoxide semiconductor films 208 b and 208 c, and the insulating film 214.For easy understanding, the energy level of the conduction band minimum(Ec) of each of the insulating film 207, the oxide semiconductor films208 a, 208 b, and 208 c, and the insulating film 214 is shown in theband structures.

In the band structure of FIG. 40A, a silicon oxide film is used as eachof the insulating film 207 and the insulating film 214, an oxidesemiconductor film formed using a metal oxide target having an atomicratio of metal elements, In:Ga:Zn=1:1:1.2, is used as the oxidesemiconductor film 208 a, an oxide semiconductor film formed using ametal oxide target having an atomic ratio of metal elements,In:Ga:Zn=4:2:4.1, is used as the oxide semiconductor film 208 b, and anoxide semiconductor film formed using a metal oxide target having anatomic ratio of metal elements, In:Ga:Zn=1:1:1.2, is used as the oxidesemiconductor film 208 c.

In the band structure of FIG. 40B, a silicon oxide film is used as eachof the insulating film 207 and the insulating film 214, an oxidesemiconductor film formed using a metal oxide target having an atomicratio of metal elements, In:Ga:Zn=4:2:4.1, is used as the oxidesemiconductor film 208 b, and an oxide semiconductor film formed using ametal oxide target having an atomic ratio of metal elements,In:Ga:Zn=1:1:1.2, is used as the oxide semiconductor film 208 c.

As illustrated in FIGS. 40A and 40B, the energy level of the conductionband minimum gradually changes between the oxide semiconductor film 208a and the oxide semiconductor film 208 b and between the oxidesemiconductor film 208 b and the oxide semiconductor film 208 c. Inother words, the energy level of the conduction band minimum iscontinuously changed or continuously connected. To obtain such a bandstructure, there exists no impurity, which forms a defect state such asa trap center or a recombination center, at the interface between theoxide semiconductor film 208 a and the oxide semiconductor film 208 b orat the interface between the oxide semiconductor film 208 b and theoxide semiconductor film 208 c.

To form a continuous junction between the oxide semiconductor film 208 aand the oxide semiconductor film 208 b and between the oxidesemiconductor film 208 b and the oxide semiconductor film 208 c, it isnecessary to form the films successively without exposure to the air byusing a multi-chamber deposition apparatus (sputtering apparatus)provided with a load lock chamber.

With the band structures of FIG. 40A and FIG. 40B, the oxidesemiconductor film 208 b serves as a well, and a channel region isformed in the oxide semiconductor film 208 b in the transistor with thelayered structure.

By providing the oxide semiconductor film 208 a and the oxidesemiconductor film 208 c, the oxide semiconductor film 208 b can bedistanced away from trap states.

In addition, the trap states might be more distant from the vacuum levelthan the energy level of the conduction band minimum (Ec) of the oxidesemiconductor film 208 b functioning as a channel region, so thatelectrons are likely to be accumulated in the trap states. When theelectrons are accumulated in the trap states, the electrons becomenegative fixed electric charge, so that the threshold voltage of thetransistor is shifted in the positive direction. Therefore, it ispreferable that the trap states be closer to the vacuum level than theenergy level of the conduction band minimum (Ec) of the oxidesemiconductor film 208 b. Such a structure inhibits accumulation ofelectrons in the trap states. As a result, the on-state current and thefield-effect mobility of the transistor can be increased.

The energy level of the conduction band minimum of each of the oxidesemiconductor films 208 a and 208 c is closer to the vacuum level thanthat of the oxide semiconductor film 208 b. Typically, a difference inenergy level between the conduction band minimum of the oxidesemiconductor film 208 b and the conduction band minimum of each of theoxide semiconductor films 208 a and 208 c is 0.15 eV or more or 0.5 eVor more and 2 eV or less or 1 eV or less. That is, the differencebetween the electron affinity of each of the oxide semiconductor films208 a and 208 c and the electron affinity of the oxide semiconductorfilm 208 b is 0.15 eV or more or 0.5 eV or more and 2 eV or less or 1 eVor less.

In such a structure, the oxide semiconductor film 208 b serves as a mainpath of a current. In other words, the oxide semiconductor film 208 bserves as a channel region, and the oxide semiconductor films 208 a and208 c serve as oxide insulating films. In addition, since the oxidesemiconductor films 208 a and 208 c each include one or more metalelements included in the oxide semiconductor film 208 b in which achannel region is formed, interface scattering is less likely to occurat the interface between the oxide semiconductor film 208 a and theoxide semiconductor film 208 b or at the interface between the oxidesemiconductor film 208 b and the oxide semiconductor film 208 c. Thus,the transistor can have high field-effect mobility because the movementof carriers is not hindered at the interface.

To prevent each of the oxide semiconductor films 208 a and 208 c fromfunctioning as part of a channel region, a material having sufficientlylow conductivity is used for the oxide semiconductor films 208 a and 208c. Thus, the oxide semiconductor films 208 a and 208 c can be referredto as oxide insulating films for such properties and/or functions.Alternatively, a material that has a smaller electron affinity (adifference in energy level between the vacuum level and the conductionband minimum) than the oxide semiconductor film 208 b and has adifference in energy level in the conduction band minimum from the oxidesemiconductor film 208 b (band offset) is used for the oxidesemiconductor films 208 a and 208 c. Furthermore, to inhibit generationof a difference in threshold voltage due to the value of the drainvoltage, it is preferable to form the oxide semiconductor films 208 aand 208 c using a material whose energy level of the conduction bandminimum is closer to the vacuum level than that of the oxidesemiconductor film 208 b. For example, a difference between the energylevel of the conduction band minimum of the oxide semiconductor film 208b and the energy level of the conduction band minimum of each of theoxide semiconductor films 208 a and 208 c is preferably greater than orequal to 0.2 eV, more preferably greater than or equal to 0.5 eV.

It is preferable that the oxide semiconductor films 208 a and 208 c nothave a spinel crystal structure. This is because if the oxidesemiconductor films 208 a and 208 c have a spinel crystal structure,constituent elements of the conductive films 212 a and 212 b might bediffused to the oxide semiconductor film 208 b at the interface betweenthe spinel crystal structure and another region. Note that each of theoxide semiconductor films 208 a and 208 c is preferably a CAAC-OS film,in which case a higher blocking property against constituent elements ofthe conductive films 212 a and 212 b, for example, copper elements, canbe obtained.

The thickness of each of the oxide semiconductor films 208 a and 208 cis greater than or equal to a thickness that is capable of inhibitingdiffusion of the constituent elements of the conductive films 212 a and212 b to the oxide semiconductor film 208 b, and less than a thicknessthat inhibits supply of oxygen from the insulating film 214 to the oxidesemiconductor film 208 b. For example, when the thickness of each of theoxide semiconductor films 208 a and 208 c is greater than or equal to 10nm, diffusion of the constituent elements of the conductive films 212 aand 212 b to the oxide semiconductor film 208 b can be inhibited. Whenthe thickness of each of the oxide semiconductor films 208 a and 208 cis less than or equal to 100 nm, oxygen can be effectively supplied fromthe insulating film 214 to the oxide semiconductor film 208 b.

Although the example where an oxide semiconductor film formed using ametal oxide target having an atomic ratio of metal elements,In:Ga:Zn=1:1:1.2, is used as each of the oxide semiconductor films 208 aand 208 c is described in this embodiment, one embodiment of the presentinvention is not limited thereto. For example, an oxide semiconductorfilm formed using a metal oxide target having an atomic ratio ofIn:Ga:Zn=1:1:1, In:Ga:Zn=1:3:2, In:Ga:Zn=1:3:4, or In:Ga:Zn=1:3:6, maybe used as each of the oxide semiconductor films 208 a and 208 c.

When the oxide semiconductor films 208 a and 208 c are formed using ametal oxide target having an atomic ratio of In:Ga:Zn=1:1:1, the oxidesemiconductor films 208 a and 208 c have an atomic ratio ofIn:Ga:Zn=1:β1 (0≤β1≤2):β2 (0<β2≤3) in some cases. When the oxidesemiconductor films 208 a and 208 c are formed using a metal oxidetarget having an atomic ratio of In:Ga:Zn=1:3:4, the oxide semiconductorfilms 208 a and 208 c have an atomic ratio of In:Ga:Zn=1:β3 (1≤β3≤5):β4(2≤β4≤6) in some cases. When the oxide semiconductor films 208 a and 208c are formed using a metal oxide target having an atomic ratio ofIn:Ga:Zn=1:3:6, the oxide semiconductor films 208 a and 208 c have anatomic ratio of In:Ga:Zn=1:β5 (1β5≤5):β6 (4≤β6≤8) in some cases.

The drawings illustrate an example where the oxide semiconductor film208 in the transistor 270 and the oxide semiconductor film 208 c in thetransistors 270A and 270B have a small thickness in a region that doesnot overlap with the conductive films 212 a and 212 b, that is, anexample where part of the oxide semiconductor film has a depressedportion. However, one embodiment of the present invention is not limitedthereto, and the oxide semiconductor film does not necessarily have adepressed region in a region that does not overlap with the conductivefilms 212 a and 212 b. FIGS. 41A and 41B illustrate examples in thiscase. FIGS. 41A and 41B are cross-sectional views illustrating anexample of the transistor. FIGS. 41A and 41B illustrate a structurewhere the oxide semiconductor film 208 in the transistor 270B does nothave a depressed portion.

As illustrated in FIGS. 41C and 41D, the oxide semiconductor film 208 cmay be formed thinner than the oxide semiconductor film 208 b inadvance, and an insulating film 219 may further be formed over the oxidesemiconductor film 208 c and the insulating film 207. In that case, anopening for connecting the oxide semiconductor film 208 c and theconductive films 212 a and 212 b is formed in the insulating film 219.The insulating film 219 can be formed with the same material and thesame forming method as the insulating film 214.

The structures of the transistors of this embodiment can be freelycombined with each other.

The structures, the methods, and the like described in this embodimentcan be combined as appropriate with any of the structures, the methods,and the like described in the other embodiments.

Embodiment 4

In this embodiment, structure examples of a light-emitting element thatcan be used as the light-emitting element 280 are described. Note thatan EL layer 1320 described in this embodiment corresponds to the ELlayer 281 described in the other embodiments.

<Structure of Light-Emitting Element>

In a light-emitting element 1330 illustrated in FIG. 42A, the EL layer1320 is sandwiched between a pair of electrodes (electrodes 1318 and1322). Note that the electrode 1318 is used as an anode and theelectrode 1322 is used as a cathode as an example in the followingdescription of this embodiment.

The EL layer 1320 includes at least a light-emitting layer and may havea stacked-layer structure including a functional layer other than thelight-emitting layer. As the functional layer other than thelight-emitting layer, a layer containing a substance having a highhole-injection property, a substance having a high hole-transportproperty, a substance having a high electron-transport property, asubstance having a high electron-injection property, a bipolar substance(a substance having high electron and hole transport properties), or thelike can be used. Specifically, functional layers such as ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer can be used in appropriatecombination.

The light-emitting element 1330 illustrated in FIG. 42A emits light whencurrent flows by applying a potential difference between the electrodes1318 and 1322 and holes and electrons are recombined in the EL layer1320. In other words, a light-emitting region is formed in the EL layer1320.

In one embodiment of the present invention, light emitted from thelight-emitting element 1330 is extracted to the outside from theelectrode 1318 side or the electrode 1322 side. Thus, one of theelectrodes 1318 and 1322 is formed using a light-transmitting substance.

Note that a plurality of EL layers 1320 may be stacked between theelectrodes 1318 and 1322 as in a light-emitting element 1331 illustratedin FIG. 42B. In the case where n (n is a natural number of 2 or more)layers are stacked, an electric charge generation layer 1320 a ispreferably provided between an m-th EL layer 1320 and an (m+1)th ELlayer 1320. Note that m is a natural number greater than or equal to 1and less than n. The components other than the electrodes 1318 and 1322correspond to the EL layer 281 of the aforementioned Embodiments.

The electric charge generation layer 1320 a can be formed using acomposite material of an organic compound and a metal oxide. Examples ofthe metal oxide are vanadium oxide, molybdenum oxide, tungsten oxide, orthe like. As the organic compound, a variety of compounds can be used;for example, an aromatic amine compound, a carbazole derivative, anaromatic hydrocarbon, and an oligomer, a dendrimer, and a polymer havinga basic skeleton of these compounds can be used. Note that as theorganic compound, it is preferable to use an organic compound that has ahole-transport property and has a hole mobility of 10⁻⁶ cm²/Vs orhigher. However, other substances may be used as long as theirhole-transport properties are higher than their electron-transportproperties. These materials used for the electric charge generationlayer 1320 a have excellent carrier-injection properties andcarrier-transport properties; thus, the light-emitting element 1331 canbe driven with low current and with low voltage. Other than thecomposite material, a material obtained by adding an alkali metal, analkaline earth metal, a compound of the alkali metal, a compound of thealkaline earth metal, or the like to the composite material can be usedfor the electric charge generation layer 1320 a.

Note that the electric charge generation layer 1320 a may be formed by acombination of a composite material of an organic compound and a metaloxide with another material. For example, the electric charge generationlayer 1320 a may be formed by a combination of a layer containing thecomposite material of an organic compound and a metal oxide with a layercontaining one compound selected from electron-donating substances and acompound having a high electron-transport property. Furthermore, theelectric charge generation layer 1320 a may be formed by a combinationof a layer containing the composite material of an organic compound anda metal oxide with a transparent conductive film.

The light-emitting element 1331 having such a structure is unlikely toresult in energy transfer between the neighboring EL layer 1320 and caneasily realize high emission efficiency and a long lifetime.Furthermore, it is easy to obtain phosphorescence from onelight-emitting layer and fluorescence from the other light-emittinglayer.

The electric charge generation layer 1320 a has a function of injectingholes to one of the EL layers 1320 that is in contact with the electriccharge generation layer 1320 a and a function of injecting electrons tothe other EL layer 1320 that is in contact with the electric chargegeneration layer 1320 a, when voltage is applied to the electrodes 1318and 1322.

The light-emitting element 1331 illustrated in FIG. 42B can provide avariety of emission colors by changing the type of the light-emittingsubstance used for the EL layers 1320. In addition, a plurality oflight-emitting substances having different emission colors may be usedas the light-emitting substances, so that light emission having a broadspectrum or white light emission can be obtained.

In the case of obtaining white light emission using the light-emittingelement 1331 in FIG. 42B, as for a combination of a plurality of ELlayers, a structure for emitting white light including red light, bluelight, and green light may be used. For example, the structure mayinclude an EL layer containing a blue fluorescent substance as alight-emitting substance and an EL layer containing green and redphosphorescent substances as light-emitting substances. Alternatively,the structure may include an EL layer emitting red light, an EL layeremitting green light, and an EL layer emitting blue light. Furtheralternatively, with a structure including EL layers emitting light ofcomplementary colors, white light emission can be obtained. In astacked-layer element including two EL layers that emit lights withcomplementary colors, the combinations of colors are as follows: blueand yellow, blue-green and red, and the like.

Note that in the structure of the above stacked-layer element, byproviding the electric charge generation layer between the stackedlight-emitting layers, the element can exhibit light emission with highluminance at a low current density, and have a long lifetime.

This embodiment can be implemented in an appropriate combination withany of the structures described in the other embodiments.

Embodiment 5

In this embodiment, a display module and electronic devices that includethe touch panel of one embodiment of the present invention is describedwith reference to FIG. 43, FIGS. 44A to 44H, and FIGS. 45A and 45B.

The touch panel of one embodiment of the present invention can be usedfor the touch panel 8004, for example.

In a display module 8000 illustrated in FIG. 43, a touch panel 8004connected to an FPC 8003, a display panel 8006 connected to an FPC 8005,a backlight 8007, a frame 8009, a printed board 8010, and a battery 8011are provided between an upper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the size of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may be formed so as to overlap with the display panel8006. A counter substrate (sealing substrate) of the display panel 8006can have a touch panel function. A photosensor may be provided in eachpixel of the display panel 8006 so that an optical touch panel can beobtained.

The backlight 8007 includes a light source 8008.

Note that although a structure in which the light source 8008 isprovided over the backlight 8007 is illustrated in FIG. 43, oneembodiment of the present invention is not limited to this structure.For example, a structure in which the light source 8008 is provided atan end portion of the backlight 8007 and a light diffusion plate isfurther provided may be employed. Note that the backlight 8007 needs notbe provided in the case where a self-luminous light-emitting elementsuch as an organic EL element is used or in the case where a reflectivepanel or the like is employed.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying electric power to the powersupply circuit, an external commercial power source or a power sourceusing the battery 8011 provided separately may be used. The battery 8011can be omitted in the case of using a commercial power source.

The display module 8000 can be additionally provided with a componentsuch as a polarizing plate, a retardation plate, or a prism sheet.

FIGS. 44A to 44H and FIGS. 45A and 45B illustrate electronic devices.These electronic devices can each include a housing 5000, a displayportion 5001, a speaker 5003, an LED lamp 5004, operation keys 5005(including a power switch or an operation switch), a connection terminal5006, a sensor 5007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 5008, and the like.

FIG. 44A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 44B illustrates a portable image reproducing device provided with arecording medium (e.g., a DVD reproducing device), which can include asecond display portion 5002, a recording medium reading portion 5011,and the like in addition to the above components. FIG. 44C illustrates atelevision device, which can include a stand 5012 and the like inaddition to the above components. The television device can be operatedby an operation switch of the housing 5000 or a separate remotecontroller 5013. With operation keys of the remote controller 5013,channels and volume can be controlled, and images displayed on thedisplay portion 5001 can be controlled. The remote controller 5013 maybe provided with a display portion for displaying data output from theremote controller 5013. FIG. 44D illustrates a portable game machine,which can include the recording medium reading portion 5011 and the likein addition to the above components. FIG. 44E illustrates a digitalcamera that has a television reception function and can include anantenna 5014, a shutter button 5015, an image receiving portion 5016,and the like in addition to the above components. FIG. 44F illustrates aportable game machine, which can include the second display portion5002, the recording medium reading portion 5011, and the like inaddition to the above components. FIG. 44G illustrates a portabletelevision receiver, which can include a charger 5017 capable oftransmitting and receiving signals, and the like in addition to theabove components. FIG. 44H illustrates a wrist-watch-type informationterminal, which can include a band 5018, a clasp 5019, and the like inaddition to the above components. The display portion 5001 mounted inthe housing 5000 also serving as a bezel includes a non-rectangulardisplay region. The display portion 5001 can display an icon 5020indicating time, another icon 5021, and the like. FIG. 45A illustrates adigital signage. FIG. 45B illustrates a digital signage mounted on acylindrical pillar.

The electronic devices illustrated in FIGS. 44A to 44H and FIGS. 45A and45B can have a variety of functions, for example, a function ofdisplaying a variety of information (e.g., a still image, a movingimage, and a text image) on a display portion, a touch panel function, afunction of displaying a calendar, date, time, and the like, a functionof controlling processing with a variety of software (programs), awireless communication function, a function of being connected to avariety of computer networks with a wireless communication function, afunction of transmitting and receiving a variety of data with a wirelesscommunication function, and a function of reading a program or datastored in a recording medium and displaying the program or data on adisplay portion. Furthermore, the electronic device including aplurality of display portions can have a function of displaying imageinformation mainly on one display portion while displaying textinformation mainly on another display portion, a function of displayinga three-dimensional image by displaying images where parallax isutilized on a plurality of display portions, or the like. Furthermore,the electronic device including an image receiving portion can have afunction of photographing a still image, a function of photographing amoving image, a function of automatically or manually correcting aphotographed image, a function of storing a photographed image in arecording medium (an external recording medium or a recording mediumincorporated in the camera), a function of displaying a photographedimage on a display portion, or the like. Note that the functions of theelectronic devices illustrated in FIGS. 44A to 44H and FIGS. 45A and 45Bare not limited thereto, and the electronic devices can have a varietyof functions.

The electronic devices in this embodiment each include a display portionfor displaying some kind of information. The touch panel of oneembodiment of the present invention can be used for the display portion.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

This application is based on Japanese Patent Application serial No.2015-081455 filed with Japan Patent Office on Apr. 13, 2015, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a transistor;a second insulating film; and a touch sensor, wherein the transistorcomprises: a gate electrode; a gate insulating film in contact with thegate electrode; a first oxide semiconductor film that is in contact withthe gate insulating film and overlaps with the gate electrode; a sourceelectrode and a drain electrode that are electrically connected to thefirst oxide semiconductor film; a first insulating film over the firstoxide semiconductor film, the source electrode, and the drain electrode;and a second oxide semiconductor film that is over the first insulatingfilm and overlaps with the first oxide semiconductor film, wherein thesecond insulating film is over the second oxide semiconductor film sothat the second oxide semiconductor film is positioned between the firstinsulating film and the second insulating film, wherein the touch sensorcomprises: a first electrode; and a second electrode, wherein one of thefirst electrode and the second electrode comprises a third oxidesemiconductor film, and wherein the second oxide semiconductor film andthe third oxide semiconductor film are formed in the same layer.
 2. Thesemiconductor device according to claim 1, wherein each thickness of thesecond oxide semiconductor film and the third oxide semiconductor filmis greater than or equal to 30 nm and less than or equal to 70 nm. 3.The semiconductor device according to claim 1, wherein the first oxidesemiconductor film, the second oxide semiconductor film, and the thirdoxide semiconductor film are each an In-M-Zn oxide, and wherein M is Al,Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf.
 4. The semiconductor deviceaccording to claim 1, wherein the first insulating film comprisesoxygen, and wherein the second insulating film comprises hydrogen. 5.The semiconductor device according to claim 1, further comprising acapacitor that comprises the second insulating film between a pair ofelectrodes, wherein the capacitor transmits visible light, and whereinone of the pair of electrodes of the capacitor comprises the third oxidesemiconductor film.
 6. The semiconductor device according to claim 5,wherein the first electrode and the second electrode each comprise thethird oxide semiconductor film.
 7. A touch panel comprising: thesemiconductor device according to claim 5; a conductive film; and aliquid crystal element, wherein the conductive film serves as a pixelelectrode, wherein the third oxide semiconductor film serves as a commonelectrode, and wherein the other of the pair of electrodes of thecapacitor comprises the conductive film.
 8. A touch panel comprising:the semiconductor device according to claim 5; a conductive film; and aliquid crystal element, wherein the third oxide semiconductor filmserves as a pixel electrode, wherein the conductive film serves as acommon electrode, and wherein the other of the pair of electrodes of thecapacitor comprises the conductive film.
 9. A touch panel comprising:the semiconductor device according to claim 1; and a light-emittingelement, wherein the light-emitting element comprises: a lowerelectrode; an upper electrode; and an EL layer positioned between thelower electrode and the upper electrode.
 10. The touch panel accordingto claim 9, wherein the first electrode and the second electrode eachcomprise the third oxide semiconductor film.
 11. The touch panelaccording to claim 9, wherein the other of the first electrode and thesecond electrode serves as the upper electrode.
 12. An electronic devicecomprising: the semiconductor device according to claim 1; and a switch,a speaker, a display portion, or a housing.
 13. An electronic devicecomprising: the touch panel according to claim 7; and a switch, aspeaker, a display portion, or a housing.
 14. A semiconductor devicecomprising: a transistor comprising a gate electrode, a gate insulatingfilm, and a first oxide semiconductor film between the gate electrodeand the gate insulating film; an insulating film over the transistor; atouch sensor comprising a first electrode and a second electrode; and acapacitor comprising the second electrode, a third electrode, and theinsulating film between the second electrode and the third electrode,wherein the capacitor transmits visible light, and wherein the secondelectrode comprises a second oxide semiconductor film.
 15. Thesemiconductor device according to claim 14, wherein a thickness of thesecond oxide semiconductor film is greater than or equal to 30 nm andless than or equal to 70 nm.
 16. The semiconductor device according toclaim 14, wherein the first oxide semiconductor film and the secondoxide semiconductor film are each an In-M-Zn oxide, and wherein M is Al,Ti, Ga, Y, Zr, La, Ce, Nd, Sn, or Hf.
 17. The semiconductor deviceaccording to claim 14, wherein the insulating film comprises hydrogen.18. A touch panel comprising: the semiconductor device according toclaim 14; and a light-emitting element, wherein the light-emittingelement comprises: a lower electrode; an upper electrode; and an ELlayer positioned between the lower electrode and the upper electrode.19. An electronic device comprising: the semiconductor device accordingto claim 14; and a switch, a speaker, a display portion, or a housing.